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What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

Search for relevant literature
Evaluate sources
Identify themes, debates and gaps
Outline the structure
Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

Quick Run-through
Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

Demonstrate your familiarity with the topic and scholarly context
Develop a theoretical framework and methodology for your research
Position yourself in relation to other researchers and theorists
Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
Body image, self-perception, self-esteem, mental health
Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

Your university’s library catalogue
Google Scholar
Project Muse (humanities and social sciences)
Medline (life sciences and biomedicine)
EconLit (economics)
Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

What question or problem is the author addressing?
What are the key concepts and how are they defined?
What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
What are the results and conclusions of the study?
How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
Themes: what questions or concepts recur across the literature?
Debates, conflicts and contradictions: where do sources disagree?
Pivotal publications: are there any influential theories or studies that changed the direction of the field?
Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

Most research has focused on young women.
There is an increasing interest in the visual aspects of social media.
But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

Look at what results have emerged in qualitative versus quantitative research
Discuss how the topic has been approached by empirical versus theoretical scholarship
Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
Critically evaluate: mention the strengths and weaknesses of your sources.
Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

To familiarise yourself with the current state of knowledge on your topic
To ensure that you’re not just repeating what others have already done
To identify gaps in knowledge and unresolved problems that your research can address
To develop your theoretical framework and methodology
To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

Cite this Scribbr article

If you want to cite this source, you can copy and paste the citation or click the ‘Cite this Scribbr article’ button to automatically add the citation to our free Reference Generator.

McCombes, S. (2022, June 07). What is a Literature Review? | Guide, Template, & Examples. Scribbr. Retrieved 6 May 2024, from https://www.scribbr.co.uk/thesis-dissertation/literature-review/

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Researching and writing for Economics students

4 literature review and citations/references.

Figure 4.1: Literature reviews and references

Your may have done a literature survey as part of your proposal. This will be incorporated into your dissertation, not left as separate stand-alone. Most economics papers include a literature review section, which may be a separate section, or incorporated into the paper’s introduction. (See organising for a standard format.)

Some disambiguation:

A ‘Literature survey’ paper: Some academic papers are called ‘literature surveys’. These try to summarise and discuss the existing work that has been done on a particular topic, and can be very useful. See, for example, works in The Journal of Economic Perspectives, the Journal of Economic Literature, the “Handbook of [XXX] Economics”

Many student projects and undergraduate dissertations are mainly literature surveys.

4.1 What is the point of a literature survey?

Your literature review should explain:

what has been done already to address your topic and related questions, putting your work in perspective, and

what techniques others have used, what are their strengths and weaknesses, and how might they be relevant tools for your own analysis.

Figure 4.2: Take notes on this as you read, and write them up.

4.2 What previous work is relevant?

Focus on literature that is relevant to your topic only.

But do not focus only on articles about your exact topic ! For example, if your paper is about the relative price of cars in the UK, you might cite papers (i) about the global automobile market, (ii) about the theory and evidence on competition in markets with similar features and (iii) using econometric techniques such as “hedonic regression” to estimate “price premia” in other markets and in other countries.

Consider: If you were Colchester a doctor and wanted to know whether a medicine would be effective for your patients, would you only consider medical studies that ran tests on Colchester residents, or would you consider more general national and international investigations?

4.3 What are “good” economics journal articles?

You should aim to read and cite peer-reviewed articles in reputable economics journals. (Journals in other fields such as Finance, Marketing and Political Science may also be useful.) These papers have a certain credibility as they have been checked by several referees and one or more editors before being published. (In fact, the publication process in Economics is extremely lengthy and difficult.)

Which journals are “reputable”? Economists spend a lot of time thinking about how to rank and compare journals (there are so many papers written about this topic that they someone could start a “Journal of Ranking Economics Journals”. For example, “ REPEC ” has one ranking, and SCIMAGO/SCOPUS has another one. You may want to focus on journals ranked in the top 100 or top 200 of these rankings. If you find it very interesting and relevant paper published somewhere that is ranked below this, is okay to cite it, but you may want to be a bit more skeptical of its findings.

Any journal you find on JSTOR is respectable, and if you look in the back of your textbooks, there will be references to articles in journals, most of which are decent.

You may also find unpublished “working papers”; these may also be useful as references. However, it is more difficult to evaluate the credibility of these, as they have not been through a process of peer review. However, if the author has published well and has a good reputation, it might be more likely that these are worth reading and citing.

Unpublished “working papers”

You may also find unpublished “working papers” or ‘mimeos’; these may also be useful as references. In fact, the publication process in Economics is so slow (six years from first working paper to publication is not uncommon) that not consulting working papers often means not being current.

However, it is more difficult to evaluate the credibility of this ‘grey literature’, as they have not been through a process of peer review. However, if the author has published well and has a good reputation, it might be more likely that these are worth reading and citing. Some working paper series are vetted, such as NBER; in terms of credibility, these might be seen as something in between a working paper and a publication.

Which of the following are “peer-reviewed articles in reputable economics journals”? Which of the following may be appropriate to cite in your literature review and in your final project? 8

Klein, G, J. (2011) “Cartel Destabilization and Leniency Programs – Empirical Evidence.” ZEW - Centre for European Economic Research Discussion Paper No. 10-107

Spencer, B. and Brander, J.A. (1983) “International R&D Rivalry and Industrial Strategy”, Review of Economic Studies Vol. 50, 707-722

Troisi, Jordan D., Andrew N. Christopher, and Pam Marek. “Materialism and money spending disposition as predictors of economic and personality variables.” North American Journal of Psychology 8.3 (2006): 421.

The Economist,. ‘Good, Bad And Ugly’. Web. 11 Apr. 2015. [accessed on…]

Mecaj, Arjola, and María Isabel González Bravo. “CSR Actions and Financial Distress: Do Firms Change Their CSR Behavior When Signals of Financial Distress Are Identified?.” Modern Economy 2014 (2014).

Universities, U. K. “Creating Prosperity: the role of higher education in driving the UK’s creative economy.” London Universities UK (2010).

4.4 How to find and access articles

You should be able to find and access all the relevant articles online. Leafing through bound volumes and photocopying should not be neededs. (Having been a student in the late 90’s and 2000’s, I wish I could get those hours back.)

Figure 4.3: The old way!

Good online tools include Jstor (jstor.org) and Google Scholar (scholar.google.co.uk). Your university should have access to Jstor, and Google is accessible to all (although the linked articles may require special access). You will usually have the ‘most access’ when logged into your university or library computing system.If you cannot access a paper, you may want to consult a reference librarian.

It is also ok, if you cannot access the journal article itself, to use the last working paper version (on Google scholar find this in the tab that says “all X versions”, where X is some number, and look for a PDF). However, authors do not always put up the most polished versions, although they should do to promote open-access. As a very last resort, you can e-mail the author and ask him or her to send you the paper.

When looking for references, try to find ones published in respected refereed economics journals (see above ).

4.5 Good starting points: Survey article, course notes, and textbooks

A “survey article” is a good place to start; this is a paper that is largely a categorization and discussion of previous work on a particular topic. You can often find such papers in journals such as

the Journal of Economic Perspectives,
the Journal of Economic Surveys,
and the Journal of Economic Literature.

These will be useful as a “catalog” of papers to read and considers citing. They are also typically very readable and offer a decent introduction to the issue or the field.

It is also helpful to consult module (course) notes and syllabi from the relevant field. Do not only limit yourself to the ones at your own university; many of universities make their course materials publicly accessible online. These will not only typically contain reading lists with well-respected and useful references, they may also contain slides and other material that will help you better understand your topic and the relevant issues.

However, be careful not to take material from course notes without properly citing it. (Better yet, try to find the original paper that the course notes are referring to.)

Textbooks serve as another extremely useful jumping off point. Look through your own textbooks and other textbooks in the right fields. Textbooks draw from, and cite a range of relevant articles and papers. (You may also want to go back to textbooks when you are finding the articles you are reading too difficult. Textbooks may present a simpler version of the material presented in an article, and explain the concepts better.)

4.6 Backwards and forwards with references

When you find a useful paper, look for its “family.” You may want to go back to earlier, more fundamental references, by looking at the articles that this paper cited. See what is listed as “keywords” (these are usually given at the top of the paper), and “JEL codes”. Check what papers this paper cites, and check what other papers cited this paper. On Google scholar you can follow this with a link “Cited by…” below the listed article. “Related articles” is also a useful link.

4.7 Citations

Keep track of all references and citations

You may find it helpful to use software to help you manage your citations

A storage “database” of citations (e.g., Jabref, Zotero, Endnote, Mendeley); these interface well with Google Scholar and Jstor

An automatic “insert citation” and “insert bibliography” in your word processing software

Use a tool like Endnote to manage and insert the bibliographies, or use a bibliography manager software such as Zotero or Jabref,

Further discussion: Citation management tools

List of works cited

Put your list of references in alphabetical order by author’s last name (surname).

Include all articles and works that you cite in your paper; do not include any that you don’t cite.

Avoiding plagiarism and academic offenses**

Here is a definition of plagiarism

The main point is that you need to cite everything that is not your own work. Furthermore, be clear to distinguish what is your own work and your own language and what is from somewhere/someone else.

Why cite? Not just to give credit to others but to make it clear that the remaining uncited content is your own.

Here are some basic rules:

(Rephrased from University of Essex material, as seen in Department of Economics, EC100 Economics for Business Handbook 2017-18, https://www1.essex.ac.uk/economics/documents/EC100-Booklet_2017.pdf accessed on 20 July 2019, pp. 15-16)

Do not submit anything that is not your own work.

Never copy from friends.

Do not copy your own work or previously submitted work. (Caveat: If you are submitting a draft or a ‘literature review and project plan’ at an earlier stage, this can be incorporated into your final submission.

Don’t copy text directly into your work, unless:

you put all passages in quotation marks: beginning with ’ and ending with ’, or clearly offset from the main text
you cite the source of this text.

It is not sufficient merely to add a citation for the source of copied material following the copied material (typically the end of a paragraph). You must include the copied material in quotation marks. … Ignorance … is no defence.’ (ibid, pp. 15 )

(‘Ibid’ means ‘same as the previous citation’.)

Your university may use sophisticated plagiarism-detection software. Markers may also report if the paper looks suspect

Before final submission, they may ask you to go over your draft and sign that you understand the contents and you have demonstrated that the work is your own.

Not being in touch with your supervisor may put you under suspicion.

Your university may give a Viva Voce oral exam if your work is under suspicion. It is a cool-sounding word but probably something you want to avoid.

Your university may store your work in its our database, and can pursue disciplinary action, even after you have graduated.

Penalties may be severe, including failure with no opportunity to retake the module (course). You may even risk your degree!

Comprehension questions; answers in footnotes

True or false: “If you do not directly quote a paper you do not need to cite it” 9

You should read and cite a paper (choose all that are correct)… 10

If it motivates ‘why your question is interesting’ and how it can be modeled economically
Only if it asks the same question as your paper
Only if it is dealing with the same country/industry/etc as you are addressing
If it has any connection to your topic, question, or related matters
If it answers a similar question as your paper
If it uses and discusses techniques that inform those you are using

4.8 How to write about previous authors’ analysis and findings

Use the right terminology.

“Johnson et al. (2000) provide an analytical framework that sheds substantial doubt on that belief. When trying to obtain a correlation between institutional efficiency and wealth per capita, they are left with largely inconclusive results.”

They are not trying to “obtain a correlation”; they are trying to measure the relationship and test hypotheses.

“Findings”: Critically examine sources

Don’t take everything that is in print (or written online) as gospel truth. Be skeptical and carefully evaluate the arguments and evidence presented. Try to really survey what has been written, to consider the range of opinions and the preponderance of the evidence. You also need to be careful to distinguish between “real research” and propaganda or press releases.

The returns to higher education in Atlantis are extremely high. For the majority of Atlanian students a university degree has increased their lifetime income by over 50%, as reported in the “Benefits of Higher Education” report put out by the Association of Atlantian Universities (2016).

But don’t be harsh without explanation:

Smith (2014) found a return to education in Atlantis exceeding 50%. This result is unlikely to be true because the study was not a very good one.

“Findings:” “They Proved”

A theoretical economic model can not really prove anything about the real world; they typically rely on strong simplifying assumptions.

Through their economic model, they prove that as long as elites have incentives to invest in de facto power, through lobbying or corruption for example, they will invest as much as possible in order to gain favourable conditions in the future for their businesses.

In their two period model, which assumes \[details of key assumptions here\] , they find that when an elite Agent has an incentive to invest in de facto power, he invests a strictly positive amount, up to the point where marginal benefit equals marginal cost”

Empirical work does not “prove” anything (nor does it claim to).

It relies on statistical inference under specific assumptions, and an intuitive sense that evidence from one situation is likely to apply to other situations.

“As Smith et al (1999) proved using data from the 1910-1920 Scandanavian stock exchange, equity prices always increase in response to reductions in corporate tax rates.”

“Smith et al (199) estimated a VAR regression for a dynamic CAP model using data from the 1910-1920 Scandanavian stock exchange. They found a strongly statistically significant negative coefficient on corporate tax rates. This suggests that such taxes may have a negative effect on publicly traded securities. However, as their data was from a limited period with several simultaneous changes in policy, and their results are not robust to \[something here\] , further evidence is needed on this question.”

Use the language of classical 11 statistics:

Hypothesis testing, statistical significance, robustness checks, magnitudes of effects, confidence intervals.

Note that generalisation outside the data depends on an intuitive sense that evidence from one situation is likely to apply to other situations.

“Findings”: How do you (or the cited paper) claim to identify a causal relationship?

This policy was explained by Smith and Johnson (2002) in their research on subsidies and redistribution in higher education. Their results showed that people with higher degree have higher salaries and so pay higher taxes. Thus subsidizing higher education leads to a large social gain.

The results the student discusses seem to show an association between higher degrees and higher salaries. The student seems to imply that the education itself led to higher salaries. This has not been shown by the cited paper. Perhaps people who were able to get into higher education would earn higher salaries anyway. There are ways economists used to try to identify a “causal effect” (by the way, this widely used term is redundant as all effects must have a cause), but a mere association between two variables is not enough

As inflation was systematically lower during periods of recession, we see that too low a level of inflation increases unemployment.

Economists have long debated the nature of this “Phillips curve” relationship. There is much work trying to determine whether the association (to the extent it exists) is a causal one. We could not rule out reverse causality, or third factor that might cause changes in both variables.

4.9 …Stating empirical results

Don’t write: “I accept the null hypothesis.”

Do write: “The results fail to reject the null hypothesis, in spite of a large sample size and an estimate with small standard errors” (if this is the case)

Note: The question of what to infer from acceptance/rejection of null hypotheses is a complex difficult one in Classical (as opposed to Bayesian) statistics. This difficulty is in part philosophical: classical hypothesis testing is deductive , while inference is necessarily inductive.

4.10 What to report

You need to read this paper more clearly; it is not clear what they conclude nor what their evidence is.

4.11 Organising your literature review

A common marking comment:

These papers seem to be discussed in random order – you need some structure organising these papers thematically, by finding, by technique, or chronologically perhaps.

How should you organise it? In what order?

Thematically (usually better)

By method, by theoretical framework, by results or assumptions, by field

Chronologically (perhaps within themes)

Exercise: Compare how the literature review section is organized in papers you are reading.

Figure 4.4: Organising a set of references

Q: What sort of structure am I using in the above outline?

It may also be helpful to make a ‘table’ of the relevant literature, as in the figure below. This will help you get a sense of the methods and results, and how the papers relate, and how to assess the evidence. You may end up putting this in the actual paper.

Figure 4.5: Organisational table from Reinstein and Riener, 2012b

4.12 What if you have trouble reading and understanding a paper?

Consult a survey paper, textbook, or lecture notes that discuss this paper and this topic

Try to find an easier related paper

Ask your supervisor for help; if he or she can

Try to understand what you can; do not try to “fake it”

4.13 Some literature survey do’s and don’ts

Do not cite irrelevant literature.

Do not merely list all the papers you could find.

Discuss them, and their relevance to your paper.

What are their strengths and weaknesses? What techniques do they use, and what assumptions do they rely on? How do they relate to each other?

Use correct citation formats.

Try to find original sources (don’t just cite a web link).

Don’t just cut and paste from other sources. And make sure to attribute every source and every quote. Be clear: which part of your paper is your own work and what is cited from others? The penalties for plagiarism can be severe!

Critically examine the sources, arguments, and methods

4.14 Comprehension questions: literature review

How to discuss empirical results: “Causal” estimation, e.g., with Instrumental Variables

Which is the best way to state it? 12

“As I prove in table 2, more lawyers lead to slower growth (as demonstrated by the regression analysis evidence).”

“Table 2 provides evidence that a high share of lawyers in a city’s population leads to slower growth.”

3.“Table 2 shows that a high share of lawyers in a city’s population is correlated with slower growth.”

Which is better? 13

“However, when a set of observable determinants of city growth (such as Census Region growth) are accounted for, the estimate of this effect becomes less precise.”
“In the correct regression I control for all determinants of city growth and find that there is no effect of lawyers on growth”

Stating empirical results: descriptive

“Using the US data from 1850-1950, I find that inflation is lower during periods of recession. This is statistically significant in a t-test [or whatever test] at the 99% level, and the difference is economically meaningful. This is consistent with the theory of …, which predicts that lower inflation increases unemployment. However, other explanations are possible, including reverse causality, and unmeasured covarying lags and trends.”

“I find a significantly lower level of inflation during periods of recession, and the difference is economically meaningful. This relationship is statistically significant and the data is accurately measured. Thus I find that inflation increases unemployment.”

Some tips on writing a good paper– relevant to literature reviews

Answer the question
Provide clear structure and signposting
Demonstrate an ability for critical analysis
Refer to your sources
Produce a coherent, clear argument
Take time to proofread for style and expresssion
Source “Assignment Writing Skills EBS 3rd year 2012”"

Answer: only b is a ‘peer reviewed article in a reputable economics journal’. All of these might be useful to cite, however. ↩

False. You need to cite any content and ideas that are not your own. ↩

Answers: 1, 5, and 6. Note that 2 and 3 are too narrow criteria, and 4 is too broad. ↩

or Bayesian if you like ↩

The second one; if this is really causal evidence. ↩

The first one. There is no ‘correct regression’. It is also not really correct in classical statistics to ‘find no effect’. ↩

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What is a literature review?

A literature review discusses published information in a particular subject area. Often part of the introduction to an essay, research report or thesis, the literature review is literally a "re" view or "look again" at what has already been written about the topic, wherein the author analyzes a segment of a published body of knowledge through summary, classification, and comparison of prior research studies, reviews of literature, and theoretical articles. Literature reviews provide the reader with a bibliographic history of the scholarly research in any given field of study. As such, as new information becomes available, literature reviews grow in length or become focused on one specific aspect of the topic.

A literature review can be just a simple summary of the sources, but usually contains an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, whereas a synthesis is a re-organization, or a reshuffling, of that information. The literature review might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. Depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

A literature review is NOT:

An annotated bibliography – a list of citations to books, articles and documents that includes a brief description and evaluation for each citation. The annotations inform the reader of the relevance, accuracy and quality of the sources cited.
A literary review – a critical discussion of the merits and weaknesses of a literary work.
A book review – a critical discussion of the merits and weaknesses of a particular book.
Teaching Information Literacy Reframed: 50+ Framework-Based Exercises for Creating Information-Literate Learners
The UNC Writing Center – Literature Reviews
The UW-Madison Writing Center: The Writer’s Handbook – Academic and Professional Writing – Learn How to Write a Literature Review

What is the difference between a literature review and a research paper?

The focus of a literature review is to summarize and synthesize the arguments and ideas of others without adding new contributions, whereas academic research papers present and develop new arguments that build upon the previously available body of literature.

How do I write a literature review?

There are many resources that offer step-by-step guidance for writing a literature review, and you can find some of them under Other Resources in the menu to the left. Writing the Literature Review: A Practical Guide suggests these steps:

Chose a review topic and develop a research question
Locate and organize research sources
Select, analyze and annotate sources
Evaluate research articles and other documents
Structure and organize the literature review
Develop arguments and supporting claims
Synthesize and interpret the literature
Put it all together

What is the purpose of writing a literature review?

Literature reviews serve as a guide to a particular topic: professionals can use literature reviews to keep current on their field; scholars can determine credibility of the writer in his or her field by analyzing the literature review.

As a writer, you will use the literature review to:

See what has, and what has not, been investigated about your topic
Identify data sources that other researches have used
Learn how others in the field have defined and measured key concepts
Establish context, or background, for the argument explored in the rest of a paper
Explain what the strengths and weaknesses of that knowledge and ideas might be
Contribute to the field by moving research forward
To keep the writer/reader up to date with current developments in a particular field of study
Develop alternative research projects
Put your work in perspective
Demonstrate your understanding and your ability to critically evaluate research in the field
Provide evidence that may support your own findings
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In This Article Expand or collapse the "in this article" section Literature Reviews

Introduction, what is a literature review.

Literature Reviews for Thesis or Dissertation
Stand-alone and Systemic Reviews
Purposes of a Literature Review
Texts on Conducting a Literature Review
Identifying the Research Topic
The Persuasive Argument
Searching the Literature
Creating a Synthesis
Critiquing the Literature
Building the Case for the Literature Review Document
Presenting the Literature Review

Other Subject Areas

Forthcoming articles expand or collapse the "forthcoming articles" section.

English as an International Language for Academic Publishing
Girls' Education in the Developing World
History of Education in Europe
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Literature Reviews by Lawrence A. Machi , Brenda T. McEvoy LAST REVIEWED: 27 October 2016 LAST MODIFIED: 27 October 2016 DOI: 10.1093/obo/9780199756810-0169

Literature reviews play a foundational role in the development and execution of a research project. They provide access to the academic conversation surrounding the topic of the proposed study. By engaging in this scholarly exercise, the researcher is able to learn and to share knowledge about the topic. The literature review acts as the springboard for new research, in that it lays out a logically argued case, founded on a comprehensive understanding of the current state of knowledge about the topic. The case produced provides the justification for the research question or problem of a proposed study, and the methodological scheme best suited to conduct the research. It can also be a research project in itself, arguing policy or practice implementation, based on a comprehensive analysis of the research in a field. The term literature review can refer to the output or the product of a review. It can also refer to the process of Conducting a Literature Review . Novice researchers, when attempting their first research projects, tend to ask two questions: What is a Literature Review? How do you do one? While this annotated bibliography is neither definitive nor exhaustive in its treatment of the subject, it is designed to provide a beginning researcher, who is pursuing an academic degree, an entry point for answering the two previous questions. The article is divided into two parts. The first four sections of the article provide a general overview of the topic. They address definitions, types, purposes, and processes for doing a literature review. The second part presents the process and procedures for doing a literature review. Arranged in a sequential fashion, the remaining eight sections provide references addressing each step of the literature review process. References included in this article were selected based on their ability to assist the beginning researcher. Additionally, the authors attempted to include texts from various disciplines in social science to present various points of view on the subject.

Novice researchers often have a misguided perception of how to do a literature review and what the document should contain. Literature reviews are not narrative annotated bibliographies nor book reports (see Bruce 1994 ). Their form, function, and outcomes vary, due to how they depend on the research question, the standards and criteria of the academic discipline, and the orthodoxies of the research community charged with the research. The term literature review can refer to the process of doing a review as well as the product resulting from conducting a review. The product resulting from reviewing the literature is the concern of this section. Literature reviews for research studies at the master’s and doctoral levels have various definitions. Machi and McEvoy 2016 presents a general definition of a literature review. Lambert 2012 defines a literature review as a critical analysis of what is known about the study topic, the themes related to it, and the various perspectives expressed regarding the topic. Fink 2010 defines a literature review as a systematic review of existing body of data that identifies, evaluates, and synthesizes for explicit presentation. Jesson, et al. 2011 defines the literature review as a critical description and appraisal of a topic. Hart 1998 sees the literature review as producing two products: the presentation of information, ideas, data, and evidence to express viewpoints on the nature of the topic, as well as how it is to be investigated. When considering literature reviews beyond the novice level, Ridley 2012 defines and differentiates the systematic review from literature reviews associated with primary research conducted in academic degree programs of study, including stand-alone literature reviews. Cooper 1998 states the product of literature review is dependent on the research study’s goal and focus, and defines synthesis reviews as literature reviews that seek to summarize and draw conclusions from past empirical research to determine what issues have yet to be resolved. Theoretical reviews compare and contrast the predictive ability of theories that explain the phenomenon, arguing which theory holds the most validity in describing the nature of that phenomenon. Grant and Booth 2009 identified fourteen types of reviews used in both degree granting and advanced research projects, describing their attributes and methodologies.

Bruce, Christine Susan. 1994. Research students’ early experiences of the dissertation literature review. Studies in Higher Education 19.2: 217–229.

DOI: 10.1080/03075079412331382057

A phenomenological analysis was conducted with forty-one neophyte research scholars. The responses to the questions, “What do you mean when you use the words literature review?” and “What is the meaning of a literature review for your research?” identified six concepts. The results conclude that doing a literature review is a problem area for students.

Cooper, Harris. 1998. Synthesizing research . Vol. 2. 3d ed. Thousand Oaks, CA: SAGE.

The introductory chapter of this text provides a cogent explanation of Cooper’s understanding of literature reviews. Chapter 4 presents a comprehensive discussion of the synthesis review. Chapter 5 discusses meta-analysis and depth.

Fink, Arlene. 2010. Conducting research literature reviews: From the Internet to paper . 3d ed. Los Angeles: SAGE.

The first chapter of this text (pp. 1–16) provides a short but clear discussion of what a literature review is in reference to its application to a broad range of social sciences disciplines and their related professions.

Grant, Maria J., and Andrew Booth. 2009. A typology of reviews: An analysis of 14 review types and associated methodologies. Health Information & Libraries Journal 26.2: 91–108. Print.

DOI: 10.1111/j.1471-1842.2009.00848.x

This article reports a scoping review that was conducted using the “Search, Appraisal, Synthesis, and Analysis” (SALSA) framework. Fourteen literature review types and associated methodology make up the resulting typology. Each type is described by its key characteristics and analyzed for its strengths and weaknesses.

Hart, Chris. 1998. Doing a literature review: Releasing the social science research imagination . London: SAGE.

Chapter 1 of this text explains Hart’s definition of a literature review. Additionally, it describes the roles of the literature review, the skills of a literature reviewer, and the research context for a literature review. Of note is Hart’s discussion of the literature review requirements for master’s degree and doctoral degree work.

Jesson, Jill, Lydia Matheson, and Fiona M. Lacey. 2011. Doing your literature review: Traditional and systematic techniques . Los Angeles: SAGE.

Chapter 1: “Preliminaries” provides definitions of traditional and systematic reviews. It discusses the differences between them. Chapter 5 is dedicated to explaining the traditional review, while Chapter 7 explains the systematic review. Chapter 8 provides a detailed description of meta-analysis.

Lambert, Mike. 2012. A beginner’s guide to doing your education research project . Los Angeles: SAGE.

Chapter 6 (pp. 79–100) presents a thumbnail sketch for doing a literature review.

Machi, Lawrence A., and Brenda T. McEvoy. 2016. The literature review: Six steps to success . 3d ed. Thousand Oaks, CA: Corwin.

The introduction of this text differentiates between a simple and an advanced review and concisely defines a literature review.

Ridley, Diana. 2012. The literature review: A step-by-step guide for students . 2d ed. Sage Study Skills. London: SAGE.

In the introductory chapter, Ridley reviews many definitions of the literature review, literature reviews at the master’s and doctoral level, and placement of literature reviews within the thesis or dissertation document. She also defines and differentiates literature reviews produced for degree-affiliated research from the more advanced systematic review projects.

Users without a subscription are not able to see the full content on this page. Please subscribe or login .

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Literature Review - what is a Literature Review, why it is important and how it is done

Strategies to Find Sources

Evaluating Literature Reviews and Sources

Reading critically, tips to evaluate sources.

Tips for Writing Literature Reviews
Writing Literature Review: Useful Sites
Citation Resources
Other Academic Writings
Useful Resources

A good literature review evaluates a wide variety of sources (academic articles, scholarly books, government/NGO reports). It also evaluates literature reviews that study similar topics. This page offers you a list of resources and tips on how to evaluate the sources that you may use to write your review.

A Closer Look at Evaluating Literature Reviews Excerpt from the book chapter, “Evaluating Introductions and Literature Reviews” in Fred Pyrczak’s Evaluating Research in Academic Journals: A Practical Guide to Realistic Evaluation , (Chapter 4 and 5). This PDF discusses and offers great advice on how to evaluate "Introductions" and "Literature Reviews" by listing questions and tips. First part focus on Introductions and in page 10 in the PDF, 37 in the text, it focus on "literature reviews".
Tips for Evaluating Sources (Print vs. Internet Sources) Excellent page that will guide you on what to ask to determine if your source is a reliable one. Check the other topics in the guide: Evaluating Bibliographic Citations and Evaluation During Reading on the left side menu.

To be able to write a good Literature Review, you need to be able to read critically. Below are some tips that will help you evaluate the sources for your paper.

Reading critically (summary from How to Read Academic Texts Critically)

Who is the author? What is his/her standing in the field.
What is the author’s purpose? To offer advice, make practical suggestions, solve a specific problem, to critique or clarify?
Note the experts in the field: are there specific names/labs that are frequently cited?
Pay attention to methodology: is it sound? what testing procedures, subjects, materials were used?
Note conflicting theories, methodologies and results. Are there any assumptions being made by most/some researchers?
Theories: have they evolved overtime?
Evaluate and synthesize the findings and conclusions. How does this study contribute to your project?

Useful links:

How to Read a Paper (University of Waterloo, Canada) This is an excellent paper that teach you how to read an academic paper, how to determine if it is something to set aside, or something to read deeply. Good advice to organize your literature for the Literature Review or just reading for classes.

Criteria to evaluate sources:

Authority : Who is the author? what is his/her credentials--what university he/she is affliliated? Is his/her area of expertise?
Usefulness : How this source related to your topic? How current or relevant it is to your topic?
Reliability : Does the information comes from a reliable, trusted source such as an academic journal?

Useful site - Critically Analyzing Information Sources (Cornell University Library)

<< Previous: Strategies to Find Sources
Next: Tips for Writing Literature Reviews >>
Last Updated: Apr 10, 2024 3:27 PM
URL: https://lit.libguides.com/Literature-Review

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The Literature Review

What is a Literature Review?
Plan Your Literature Review
Identify a Research Gap
Define Your Research Question
Search the Literature
Analyze Your Research Results
Manage Research Results
Write the Literature Review

What is a Literature Review? What is its purpose?

The purpose of a literature review is to offer a comprehensive review of scholarly literature on a specific topic along with an evaluation of the strengths and weaknesses of authors' arguments . In other words, you are summarizing research available on a certain topic and then drawing conclusions about researchers' findings. To make gathering research easier, be sure to start with a narrow/specific topic and then widen your topic if necessary.

A thorough literature review provides an accurate description of current knowledge on a topic and identifies areas for future research. Are there gaps or areas that require further study and exploration? What opportunities are there for further research? What is missing from my collection of resources? Are more resources needed?

It is important to note that conclusions described in the literature you gather may contradict each other completely or in part. Recognize that knowledge creation is collective and cumulative. Current research is built upon past research findings and discoveries. Research may bring previously accepted conclusions into question. A literature review presents current knowledge on a topic and may point out various academic arguments within the discipline.

What a Literature Review is not

A literature review is not an annotated bibliography . An annotated bibliography provides a brief summary, analysis, and reflection of resources included in the bibliography. Often it is not a systematic review of existing research on a specific subject. That said, creating an annotated bibliography throughout your research process may be helpful in managing the resources discovered through your research.
A literature review is not a research paper . A research paper explores a topic and uses resources discovered through the research process to support a position on the topic. In other words, research papers present one side of an issue. A literature review explores all sides of the research topic and evaluates all positions and conclusions achieved through the scientific research process even though some conclusions may conflict partially or completely.

From the Online Library

SAGE Research Methods is a web-based research methods tool that covers quantitative, qualitative and mixed methods. Researchers can explore methods and concepts to help design research projects, understand a particular method or identify a new method, and write up research. Sage Research Methods focuses on methodology rather than disciplines, and is of potential use to researchers from the social sciences, health sciences and other research areas.

Sage Research Methods Project Planner - Reviewing the Literature View the resources and videos for a step-by-step guide to performing a literature review.

The Literature Review: Step by Step

Follow this step-by-step process by using the related tabs in this Guide.

Define your Research question
Analyze the material you’ve found
Manage the results of your research
Write your Review

Getting Started

Consider the following questions as you develop your research topic, conduct your research, and begin evaluating the resources discovered in the research process:

What is known about the subject?
Are there any gaps in the knowledge of the subject?
Have areas of further study been identified by other researchers that you may want to consider?
Who are the significant research personalities in this area?
Is there consensus about the topic?
What aspects have generated significant debate on the topic?
What methods or problems were identified by others studying in the field and how might they impact your research?
What is the most productive methodology for your research based on the literature you have reviewed?
What is the current status of research in this area?
What sources of information or data were identified that might be useful to you?
How detailed? Will it be a review of ALL relevant material or will the scope be limited to more recent material, e.g., the last five years.
Are you focusing on methodological approaches; on theoretical issues; on qualitative or quantitative research?

What is Academic Literature?

What is the difference between popular and scholarly literature?

To better understand the differences between popular and scholarly articles, comparing characteristics and purpose of the publications where these articles appear is helpful.

Database Search Tips

Boolean Operators
Keywords vs. Subjects
Creating a Search String
Library databases are collections of resources that are searchable, including full-text articles, books, and encyclopedias.
Searching library databases is different than searching Google. Best results are achieved when using Keywords linked with Boolean Operators .
Applying Limiters such as full-text, publication date, resource type, language, geographic location, and subject help to refine search results.
Utilizing Phrases or Fields , in addition to an awareness of Stop Words , can focus your search and retrieve more useful results.
Have questions? Ask a Librarian

Boolean Operators connect keywords or concepts logically to retrieve relevant articles, books, and other resources. There are three Boolean Operators:

Using AND

Narrows search results
Connects two or more keywords/concepts
All keywords/concepts connected with "and" must be in an article or resource to appear in the search results list

Venn diagram of the AND connector

Example: The result list will include resources that include both keywords -- "distracted driving" and "texting" -- in the same article or resource, represented in the shaded area where the circles intersect (area shaded in purple).

Broadens search results ("OR means more!")
Connects two or more synonyms or related keywords/concepts
Resources appearing in the results list will include any of the terms connected with the OR connector

Venn diagram of the OR connector

Example: The result list will include resources that include the keyword "texting" OR the keyword "cell phone" (entire area shaded in blue); either is acceptable.

Excludes keywords or concepts from the search
Narrows results by removing resources that contain the keyword or term connected with the NOT connector
Use sparingly

Venn diagram of the NOT connector

Example: The result list will include all resources that include the term "car" (green area) but will exclude any resource that includes the term "motorcycle" (purple area) even though the term car may be present in the resource.

A library database searches for keywords throughout the entire resource record including the full-text of the resource, subject headings, tags, bibliographic information, etc.

Natural language words or short phrases that describe a concept or idea
Can retrieve too few or irrelevant results due to full-text searching (What words would an author use to write about this topic?)
Provide flexibility in a search
Must consider synonyms or related terms to improve search results
TIP: Build a Keyword List

Example: The keyword list above was developed to find resources that discuss how texting while driving results in accidents. Notice that there are synonyms (texting and "text messaging"), related terms ("cell phones" and texting), and spelling variations ("cell phone" and cellphone). Using keywords when searching full text requires consideration of various words that express an idea or concept.

Subject Headings
Predetermined "controlled vocabulary" database editors apply to resources to describe topical coverage of content
Can retrieve more precise search results because every article assigned that subject heading will be retrieved.
Provide less flexibility in a search
Can be combined with a keyword search to focus search results.
TIP: Consult database subject heading list or subject headings assigned to relevant resources

Example 1: In EBSCO's Academic Search Complete, clicking on the "Subject Terms" tab provides access to the entire subject heading list used in the database. It also allows a search for specific subject terms.

Example 2: A subject term can be incorporated into a keyword search by clicking on the down arrow next to "Select a Field" and selecting "Subject Terms" from the dropdown list. Also, notice how subject headings are listed below the resource title, providing another strategy for discovering subject headings used in the database.

When a search term is more than one word, enclose the phrase in quotation marks to retrieve more precise and accurate results. Using quotation marks around a term will search it as a "chunk," searching for those particular words together in that order within the text of a resource.

"cell phone"

"distracted driving"

"car accident"

TIP: In some databases, neglecting to enclose phrases in quotation marks will insert the AND Boolean connector between each word resulting in unintended search results.

Truncation provides an option to search for a root of a keyword in order to retrieve resources that include variations of that word. This feature can be used to broaden search results, although some results may not be relevant. To truncate a keyword, type an asterisk (*) following the root of the word.

For example:

Library databases provide a variety of tools to limit and refine search results. Limiters provide the ability to limit search results to resources having specified characteristics including:

Resource type
Publication date
Geographic location

In both the EBSCO and ProQuest databases, the limiting tools are located in the left panel of the results page.

EBSCO ProQuest

The short video below provides a demonstration of how to use limiters to refine a list of search results.

Each resource in a library database is stored in a record. In addition to the full-text of the resources, searchable Fields are attached that typically include:

Journal title
Date of Publication

Incorporating Fields into your search can assist in focusing and refining search results by limiting the results to those resources that include specific information in a particular field.

In both EBSCO and ProQuest databases, selecting the Advanced Search option will allow Fields to be included in a search.

For example, in the Advanced Search option in EBSCO's Academic Search Complete database, clicking on the down arrow next to "Select a Field" provides a list of fields that can be searched within that database. Select the field and enter the information in the text box to the left to use this feature.

Stop words are short, commonly used words--articles, prepositions, and pronouns-- that are automatically dropped from a search. Typical stop words include:

In library databases, a stop word will not be searched even if it is included in a phrase enclosed in quotation marks. In some instances, a word will be substituted for the stop word to allow for the other words in the phrase to be searched in proximity to one another within the text of the resource.

For example, if you searched company of America, your result list will include these variatons:

company in America
company of America
company for America

Creating an Search String

This short video demonstrates how to create a search string -- keywords connected with Boolean operators -- to use in a library database search to retrieve relevant resources for any research assignment.

Database Search Menu Template Use this search menu template to plan a database search.
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CAREER FEATURE
04 December 2020
Correction 09 December 2020

How to write a superb literature review

Andy Tay is a freelance writer based in Singapore.

You can also search for this author in PubMed Google Scholar

Literature reviews are important resources for scientists. They provide historical context for a field while offering opinions on its future trajectory. Creating them can provide inspiration for one’s own research, as well as some practice in writing. But few scientists are trained in how to write a review — or in what constitutes an excellent one. Even picking the appropriate software to use can be an involved decision (see ‘Tools and techniques’). So Nature asked editors and working scientists with well-cited reviews for their tips.

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doi: https://doi.org/10.1038/d41586-020-03422-x

Interviews have been edited for length and clarity.

Updates & Corrections

Correction 09 December 2020 : An earlier version of the tables in this article included some incorrect details about the programs Zotero, Endnote and Manubot. These have now been corrected.

Hsing, I.-M., Xu, Y. & Zhao, W. Electroanalysis 19 , 755–768 (2007).

Article Google Scholar

Ledesma, H. A. et al. Nature Nanotechnol. 14 , 645–657 (2019).

Article PubMed Google Scholar

Brahlek, M., Koirala, N., Bansal, N. & Oh, S. Solid State Commun. 215–216 , 54–62 (2015).

Choi, Y. & Lee, S. Y. Nature Rev. Chem . https://doi.org/10.1038/s41570-020-00221-w (2020).

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Literature Review: A Definition

What is a literature review, then.

A literature review discusses and analyses published information in a particular subject area. Sometimes the information covers a certain time period.

A literature review is more than a summary of the sources, it has an organizational pattern that combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

While the main focus of an academic research paper is to support your own argument, the focus of a literature review is to summarize and synthesize the arguments and ideas of others. The academic research paper also covers a range of sources, but it is usually a select number of sources, because the emphasis is on the argument. Likewise, a literature review can also have an "argument," but it is not as important as covering a number of sources. In short, an academic research paper and a literature review contain some of the same elements. In fact, many academic research papers will contain a literature review section. What aspect of the study (either the argument or the sources) that is emphasized determines what type of document it is.

( "Literature Reviews" from The Writing Center, University of North Carolina at Chapel Hill )

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone.

For professionals, they are useful reports that keep them up to date with what is current in the field.

For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper's investigation.

Comprehensive knowledge of the literature of the field is essential to most research papers.

Journal Articles on Writing Literature Reviews

Research Methods for Comprehensive Science Literature Reviews Author: Brown,Barry N. Journal: Issues in Science & Technology Librarianship Date: Spring2009 Issue: 57 Page: 1 more... less... Finding some information on most topics is easy. There are abundant sources of information readily available. However, completing a comprehensive literature review on a particular topic is often difficult, laborious, and time intensive; the project requires organization, persistence, and an understanding of the scholarly communication and publishing process. This paper briefly outlines methods of conducting a comprehensive literature review for science topics. [ABSTRACT FROM AUTHOR];
Research: Considerations in Writing a Literature Review Authors: Black,K. Journal: The New Social Worker Date: 01/01; 2007 Volume: 14 Issue: 2 Page: 12 more... less... Literature reviews are ubiquitous in academic journals, scholarly reports, and social work education. Conducting and writing a good literature review is both personally and professionally satisfying. (Journal abstract).
How to do (or not to do) A Critical Literature Review Authors: Jesson,Jill; Lacey,Fiona Journal: Pharmacy Education Pub Date: 2006 Volume: 6 Issue: 2 Pages:139 - 148 more... less... More and more students are required to perform a critical literature review as part of their undergraduate or postgraduate studies. Whilst most of the latest research methods textbooks advise how to do a literature search, very few cover the literature review. This paper covers two types of review: a critical literature review and a systematic review. [ABSTRACT FROM AUTHOR]
Conducting a Literature Review Authors: Rowley,Jennifer; Slack,Frances Journal: Management Research News Pub Date: 2004 Volume: 27 Issue: 6 Pages:31-39 more... less... Abstract: This article offers support and guidance for students undertaking a literature review as part of their dissertation during an undergraduate or Masters course. A literature review is a summary of a subject field that supports the identification of specific research questions. A literature review needs to draw on and evaluate a range of different types of sources including academic and professional journal articles, books, and web-based resources. The literature search helps in the identification and location of relevant documents and other sources. Search engines can be used to search web resources and bibliographic databases. Conceptual frameworks can be a useful tool in developing an understanding of a subject area. Creating the literature review involves the stages of: scanning, making notes, structuring the literature review, writing the literature review, and building a bibliography.

Some Books from the WU Catalog

The SAGE handbook of visual research methods [electronic resource] by Edited by Luc Pauwels and Dawn Mannay. ISBN: 9781526417015 Publication Date: SAGE Publications, Inc., 2020.

Helpful Websites

"How to do a Literature Review" from Ferdinand D. Bluford Library
"The Literature Review: A Few Tips on Conducting It." from the University of Toronto
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Literature review.

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Reviewing the Literature: Why do it?

Personal: To familiarize yourself with a new area of research, to get an overview of a topic, so you don't want to miss something important, etc.
Required writing for a journal article, thesis or dissertation, grant application, etc.

Literature reviews vary; there are many ways to write a literature review based on discipline, material type, and other factors.

Background:

Literature Reviews - UNC Writing Center
Literature Reviews: An Overview for Graduate Students - What is a literature review? What purpose does it serve in research? What should you expect when writing one? - NCSU Video

Where to get help (there are lots of websites, blogs , articles, and books on this topic) :

The Center for writing and Communicating Ideas (CWCI)
(these are non-STEM examples: dissertation guidance , journal guidelines )
How to prepare a scientific doctoral dissertation based on research articles (2012)
Writing a graduate thesis or dissertation (2016)
The good paper : a handbook for writing papers in higher education (2015)
Proposals that work : a guide for planning dissertations and grant proposals (2014)
Theses and dissertations : a guide to planning, research, and writing (2008)
Talk to your professors, advisors, mentors, peers, etc. for advice

READ related material and pay attention to how others write their literature reviews:

Dissertations
Journal articles
Grant proposals
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3.1. Hoops and Barriers
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4.1. Introduction to Literature Reviews
4.2. What is a Literature Review?
4.3. How to Get Started
4.4. Where to Find the Literature
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What is a Literature Review?

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Tools and Settings

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Learning Objectives

At the conclusion of this chapter, you will be able to:

Recognize how information is created and how it evolves over time;
Identify how the information cycle impacts the reliability of the information;
Select information sources appropriate to information need.

Overview of information

Because a literature review is a summary and analysis of the relevant publications on a topic, we first have to understand what is meant by ‘the literature’. In this case, ‘the literature’ is a collection of all of the relevant written sources on a topic. It will include both theoretical and empirical works. Both types provide scope and depth to a literature review.

Disciplines of knowledge

When drawing boundaries around an idea, topic, or subject area, it helps to think about how and where the information for the field is produced. For this, you need to identify the disciplines of knowledge production in a subject area.

Information does not exist in the environment like some kind of raw material. It is produced by individuals working within a particular field of knowledge who use specific methods for generating new information. Disciplines are knowledge-producing and -disseminating systems which consume, produce, and disseminate knowledge. Looking through a course catalog of a post-secondary educational institution gives clues to the structure of a discipline structure. Fields such as political science, biology, history and mathematics are unique disciplines, as are education and nursing, with their own logic for how and where new knowledge is introduced and made accessible.

You will need to become comfortable with identifying the disciplines that might contribute information to any search strategy. When you do this, you will also learn how to decode the way how people talk about a topic within a discipline. This will be useful to you when you begin a review of the literature in your area of study.

For example, think about the disciplines that might contribute information a the topic such as the role of sports in society. Try to anticipate the type of perspective each discipline might have on the topic. Consider the following types of questions as you examine what different disciplines might contribute:

What is important about the topic to the people in that discipline?
What is most likely to be the focus of their study about the topic?
What perspective would they be likely to have on the topic?

What would be some key questions or issues related to the topic in education?

how schools privilege or punish student athletes
how young people are socialized into the ideal of team cooperation
differences between boys’ and girls’ participation in organized sports

We see that a single topic can be approached from many different perspectives depending on how the disciplinary boundaries are drawn and how the topic is framed. This step of the research process requires you to make some decisions early on to focus the topic on a manageable and appropriate scope for the rest of the strategy ( Hansen & Paul, 2015 [https://edtechbooks.org/-MUq] ).

‘The literature’ consists of the published works that document a scholarly conversation in a field of study. You will find, in ‘the literature,’ documents that explain the background of your topic so the reader knows where you found loose ends in the established research of the field and what led you to your own project. Although your own literature review will focus on primary, peer-reviewed resources, it will begin by first grounding yourself in background subject information generally found in secondary and tertiary sources such as books and encyclopedias. Once you have that essential overview, you delve into the seminal literature of the field. As a result, while your literature review may consist of research articles tightly focused on your topic with secondary and tertiary sources used more sparingly, all three types of information (primary, secondary, tertiary) are critical to your research.

Definitions

Theoretical – discusses a theory, conceptual model or framework for understanding a problem.
Empirical – applies theory to a behavior or event and reports derived data to findings.
Seminal – “A classic work of research literature that is more than 5 years old and is marked by its uniqueness and contribution to professional knowledge” ( Houser, 4th ed., 2018, p. 112 [https://edtechbooks.org/-MUq] ).
Practical – “…accounts of how things are done” ( Wallace & Wray, 3rd ed., 2016, p. 20 [https://edtechbooks.org/-MUq] ). Action research, in Education, refers to a wide variety of methods used to develop practical solutions. ( Great Schools Partnership, 2017 [https://edtechbooks.org/-MUq] ).
Policy – generally produced by policy-makers, such as government agencies.
Primary – published results of original research studies .
Secondary – interpret, discuss, summarize original sources
Tertiary – synthesize or distill primary and secondary sources. Examples include: encyclopedias, directories, dictionaries, handbooks, guides, classification, chronology, and other fact books.
Grey literature – research and information released by non-commercial publishers, such as government agencies, policy organizations, and think-tanks.

‘The literature’ is published in books, journal articles, conference proceedings, theses and dissertations. It can also be found in newspapers, encyclopedias, textbooks, as well as websites and reports written by government agencies and professional organizations. While these formats may contain what we define as ‘the literature’, not all of it will be appropriate for inclusion in your own literature review.

These sources are found through different tools that we will discuss later in this section. Although a discovery tool, such as a database or catalog, may link you to the ‘the literature’ not every tool is appropriate to every literature review. No single source will have all of the information resources you should consult. A comprehensive literature review should include searches in the following:

Multiple subject and article databases
Library and other book catalogs
Grey literature sources [https://edtechbooks.org/-Po]

Information Cycle

To get a better idea of how the literature in a discipline develops, it’s useful to see how the information publication lifecycle works. These distinct stages show how information is created, reviewed, and distributed over time.

The following chart can be used to guide you in searching literature existing at various stages of the scholarly communication process (freely accessible sources are linked, subscription or subscribed sources are listed but not linked):

shows a continuous circle containing six bubbles that illustrate how an idea for a research study proceeds through evaluation for quality by peers to publication. After publication, the study is disseminated in print or electronic form and accessed through libraries, vendors, and the web. Preservation and reuse make up the remaining bubbles.

Information Types

To continue our discussion of information sources, there are two ways published information in the field can be categorized:

Articles by the type of periodical in which an article it is published, for example, magazine, trade, or scholarly publications .
Where the material is located in the information cycle, as in primary, secondary, or tertiary information sources .

Popular, Trade, or Scholarly publications

Types of periodicals.

Journals, trade publications, and magazines are all periodicals, and articles from these publications they can all look similar article by article when you are searching in the databases. It is good to review the differences and think about when to use information from each type of periodical.

A magazine is a collection of articles and images about diverse topics of popular interest and current events.

Features of magazines:

articles are usually written by journalists
articles are written for the average adult
articles tend to be short
articles rarely provides a list of reference sources at the end of the article
lots of color images and advertisements
the decision about what goes into the magazine is made by an editor or publisher
magazines can have broad appeal, like Time and Newsweek , or a narrow focus, like Sports Illustrated and Mother Earth News .

Popular magazines like Psychology Today , Sports Illustrated , and Rolling Stone can be good sources for articles on recent events or pop-culture topics, while Harpers , Scientific American , and The New Republic will offer more in-depth articles on a wider range of subjects. These articles are geared towards readers who, although not experts, are knowledgeable about the issues presented.

Trade Publications

Trade publications or trade journals are periodicals directed to members of a specific profession. They often have information about industry trends and practical information for people working in the field.

Features of trade publications:

Authors are specialists in their fields
Focused on members of a specific industry or profession
No peer review process
Include photographs, illustrations, charts, and graphs, often in color
Technical vocabulary

Trade publications are geared towards professionals in a discipline. They report news and trends in a field, but not original research. They may provide product or service reviews, job listings, and advertisements.

Scholarly, Academic, and Scientific Publications

Scholarly, academic, and scientific publications are a collections of articles written by scholars in an academic or professional field. Most journals are peer-reviewed or refereed, which means a panel of scholars reviews articles to decide if they should be accepted into a specific publication. Journal articles are the main source of information for researchers and for literature reviews.

Features of journals:

written by scholars and subject experts
author’ credentials and institution will be identified
written for other scholars
dedicated to a specific discipline that it covers in depth
often report on original or innovative research
long articles, often 5-15 pages or more
articles almost always include a list of sources at the end (Works Cited, References, Sources, or Bibliography) that point back to where the information was derived
no or very few advertisements
published by organizations or associations to advance their specialized body of knowledge

Scholarly journals provider articles of interest to experts or researchers in a discipline. An editorial board of respected scholars (peers) reviews all articles submitted to a journal. They decide if the article provides a noteworthy contribution to the field and should be published. There are typically few little or no advertisements. Articles published in scholarly journals will include a list of references.

A word about open access journals

Increasingly, scholars are publishing findings and original research in open access journals . Open access journals are scholarly and peer-reviewed and open access publishers provide unrestricted access and unrestricted use. Open access is a means of disseminating scholarly research that breaks from the traditional subscription model of academic publishing. It is free of charge to readers and because it is online, it is available at anytime, anywhere in the world, to anyone with access to the internet. The Directory of Open Access Journals ( DOAJ [https://doaj.org/] ) indexes and provides access to high-quality, peer-reviewed scholarly articles.

In summary, newspapers and other popular press publications are useful for getting general topic ideas. Trade publications are useful for practical application in a profession and may also be a good source of keywords for future searching. Scholarly journals are the conversation of the scholars who are doing research in a specific discipline and publishing their research findings.

Primary, Secondary, and Tertiary Sources

Primary sources of information are those types of information that come first. Some examples of primary sources are:

original research, like data from an experiment with plankton.
diaries, journals, photographs
data from the census bureau or a survey you have done
original documents, like the constitution or a birth certificate
newspapers are primary sources when they report current events or current opinion
speeches, interviews, email, letters
religious books
personal memoirs and autobiographies
pottery or weavings

There are different types of primary sources for different disciplines. In the discipline of history, for example, a diary or transcript of a speech is a primary source. In education and nursing, primary sources will generally be original research, including data sets.

Secondary sources are written about primary sources to interpret or analyze them. They are a step or more removed from the primary event or item. Some examples of secondary sources are:

commentaries on speeches
critiques of plays, journalism, or books
a journal article that talks about a primary source such as an interpretation of Steinbeck’s The Grapes of Wrath, or the flower symbolism of Monet’s water garden paintings
textbooks (can also be considered tertiary)
biographies
encyclopedias

Tertiary sources are further removed from the original material and are a distillation and collection of primary and secondary sources. Some examples are:

bibliography of critical works about an author
textbooks (also considered secondary)

A comparison of information sources across disciplines:

Information Sources

In this section, we discuss how to find not only information, but the sources of information in your discipline or topic area. As we see in the graphic and chart above, the information you need for your literature review will be located in multiple places. How and where research and publication occurs drives how and where the information is located, which in turn determines how you will discover and retrieve it. When we talk about information sources for a literature review in education or nursing, we generally mean these five areas: the internet, reference material and other books, empirical or evidence-based articles in scholarly, peer-reviewed journals, conference proceedings and papers, dissertations and theses, and grey literature.

The internet can be an excellent place to satisfy some initial research needs.

It is a good resource for background information and for finding keywords for searching in the library catalog and databases.
It is a good tool for locating professional organizations and searching for information and the names of experts in a given discipline.
Google Scholar [https://scholar.google.com/] is a useful discovery tool for citations, especially if you are trying to get the lay of the land surrounding your topic or if you are having a problem with keywords in the databases. You can find some information to refine your search terms. It is NOT acceptable to depend on Google Scholar for finding articles because of the spotty coverage and lack of adequate search features.

Books and Reference Sources

Reference materials and books are available in both print and electronic formats. They provide gateway knowledge to a subject area and are useful at the beginning of the research process to:

Get an overview of the topic, learn the scope, key definitions, significant figures who are involved, and important timelines;
Discover the foundations of a topic;
Learn essential definitions, vocabulary terms, and keywords you can use in your literature searching strategy.

Scholarly Articles in Journals

Another major category of information sources is scholarly information produced by subject experts working in academic institutions, research centers, and scholarly organizations. Scholars and researchers generate information that advances our knowledge and understanding of the world. The research they do creates new opportunities for inventions, practical applications, and new approaches to solving problems or understanding issues.

Academics, researchers and students at universities make their contributions to scholarly knowledge available in many forms:

masters’ theses
doctoral dissertations
conference papers
journal articles and books
individual scholars’ web pages
web pages developed by the researcher’s home institution (Hansen & Paul, 2015).

Scholars and researchers introduce their discoveries to the world in a formal system of information dissemination that has developed over centuries. Because scholarly research undergoes a process of “peer review” before being published (meaning that other experts review the work and pass judgment about whether it is worthy of publication), the information you find from scholarly sources meets preset standards for accuracy, credibility and validity in that field.

Likewise, scholarly journal articles are generally considered to be among the most reliable sources of information because they have gone through a peer-review process.

Conference Papers & Proceedings

Conferences are a major source of emerging research where researchers present papers on their current research and obtain feedback from the audience. The papers presented in the conference are then usually published in a volume called a conference proceeding. Conference proceedings highlight current discussion in a discipline and can lead you to scholars who are interested in specific research areas.

A word about conference papers: several factors contribute to making these documents difficult to find. It may be months before a paper is published as a journal article, or it may never be published. Publishers and professional associations are inconsistent in how they publish proceedings. For example, the papers from an annual conference may be published as individual, stand-alone titles, which may be indexed in a library catalog, or the conference proceedings may be treated more like a periodical or serial and, therefore, indexed in a journal database.

It is not unusual that papers delivered at professional conferences are not published in print or electronic form, although an abstract may be available. In these cases, the full paper may only be available from the author or authors.

The most important thing to remember is that if you have any difficulty finding a conference proceeding or paper, ask a librarian for assistance.

Dissertations and Theses

Dissertations and theses can be rich sources of information and have extensive reference lists to scan for resources. They are considered gray literature, so are not “peer reviewed”. The accuracy and validity of the paper itself may depend on the school that awarded the doctoral or master’s degree to the author.

In thinking about ‘the literature’ of your discipline, you are beginning the first step in writing your own literature review. By understanding what the literature in your field is, as well as how and when it is generated, you begin to know what is available and where to look for it.

We briefly discussed seven types of (sometimes overlapping) information:

information found on the web
information found in reference books and monographs
information found in scholarly journals
information found in conference proceedings and papers
information found in dissertations and theses
information found in magazines and trade journals
information that is primary, secondary, or tertiary.

By conceptualizing or scoping how and where the literature of your discipline or topic area is generated, you have started on your way to writing your own literature review.

illustrates what skills are needed to find what is available on a topic. Students should be able to understand, know, and recognize different types of information, the publication process, issues of accessibility, and what services are available to help them. In this way, students are able to identify different types of information, available search tools, different information formats, and use new tools as they become available.

Finally, remember:

“All information sources are not created equal. Sources can vary greatly in terms of how carefully they are researched, written, edited, and reviewed for accuracy. Common sense will help you identify obviously questionable sources, such as tabloids that feature tales of alien abductions, or personal websites with glaring typos. Sometimes, however, a source’s reliability—or lack of it—is not so obvious…You will consider criteria such as the type of source, its intended purpose and audience, the author’s (or authors’) qualifications, the publication’s reputation, any indications of bias or hidden agendas, how current the source is, and the overall quality of the writing, thinking, and design.” ( Writing for Success, 2015, p. 448 [https://edtechbooks.org/-MUq] ).

We will cover how to evaluate sources in more detail in a later chapter.

For each of these information needs, indicate what resources would be the best fit to answer your question. There may be more than one source so don’t feel like you have to limit yourself to only one. See Answer Key for the correct response.

You are to write a brief paper on a theory that you only vaguely understand. You need some basic information. Where would you look?
If you heard something on the radio about a recent research involving an herbal intervention for weight loss where could you find the actual study?
You are going to be doing an internship in a group home for young men. You have heard that one issue that comes up for them is anger. Where would you look for practical interventions to help you manage this problem if it came up?
You have the opportunity to work on a research project through a grant proposal. You need to justify the research question and show that there is an interest and a need for this research. What resources would you cite in your application?
You have been assigned a project to find primary sources about classroom discipline used in early 20th-century schools. What primary sources could you use and where would you find them?
You have an idea for a great thesis but you are afraid that it has been done before. Since you would like to do something original, where could you find out if someone else has done the project?
There was a post on Facebook that welfare recipients in Arizona were recently tested for drug use with only three in 140,000 having positive results. Where can I find out if this number is accurate?

Test Yourself

Match the type of periodical to its content

Trade publication

Contains articles about a variety of topics of popular interest; also contains advertising.
Has information about industry trends and practical information for professionals in a field.
Contains articles written by scholars in an academic field and reviewed by experts in that field.

Scholarly journal

Given what you know about information types and sources, which of the following is the most accurate and reliable.

Books and encyclopedias.
News broadcasts and social media directly following an event.
Analysis of an event in the news media or popular magazine weeks after an event.
Articles written by scholars and published in a journal.

Given what you know about information types and sources, which of the following is the least accurate and reliable.

What is information called that is either a diary, a speech, original research, data, artwork, or a religious book.

To find the best information in the databases you need to use keywords that are used by the scholars. Where do you find out what keywords to try?

From websites
In journal articles

Which of the following is NOT true about scholarly journals?

They contain the conversation of the scholars on a particular subject.
They are of interest to the general public.
The articles are followed by an extensive reference list.
They contain reports of original research.

Linda Frederiksen is the Head of Access Services at Washington State University Vancouver. She has a Master of Library Science degree from Emporia State University in Kansas. Linda is active in local, regional and national organizations, projects and initiatives advancing open educational resources and equitable access to information.

Sue F. Phelps is the Health Sciences and Outreach Services Librarian at Washington State University Vancouver. Her research interests include information literacy, accessibility of learning materials for students who use adaptive technology, diversity and equity in higher education, and evidence based practice in the health sciences

Brigham Young University

This content is provided to you freely by BYU Open Learning Network.

Access it online or download it at https://open.byu.edu/rapidwriting/what_is_lit_review .

Methodological Approaches to Literature Review

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First Online: 15 October 2023
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Dennis Thomas 2 ,
Elida Zairina 3 &
Johnson George 4

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The literature review can serve various functions in the contexts of education and research. It aids in identifying knowledge gaps, informing research methodology, and developing a theoretical framework during the planning stages of a research study or project, as well as reporting of review findings in the context of the existing literature. This chapter discusses the methodological approaches to conducting a literature review and offers an overview of different types of reviews. There are various types of reviews, including narrative reviews, scoping reviews, and systematic reviews with reporting strategies such as meta-analysis and meta-synthesis. Review authors should consider the scope of the literature review when selecting a type and method. Being focused is essential for a successful review; however, this must be balanced against the relevance of the review to a broad audience.

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Thomas, D., Zairina, E., George, J. (2023). Methodological Approaches to Literature Review. In: Babar, ZUD. (eds) Encyclopedia of Evidence in Pharmaceutical Public Health and Health Services Research in Pharmacy. Springer, Cham. https://doi.org/10.1007/978-3-030-64477-2_57

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Quantitative research: literature review .

Archer Library This link opens in a new window
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Research & Statistics
Literature Review Resources
Citations & Reference

Exploring the literature review

Literature review model: 6 steps.

Adapted from The Literature Review , Machi & McEvoy (2009, p. 13).

Your Literature Review

Step 2: search, boolean search strategies, search limiters, ★ ebsco & google drive.

1. Select a Topic

"All research begins with curiosity" (Machi & McEvoy, 2009, p. 14)

Selection of a topic, and fully defined research interest and question, is supervised (and approved) by your professor. Tips for crafting your topic include:

Be specific. Take time to define your interest.
Topic Focus. Fully describe and sufficiently narrow the focus for research.
Academic Discipline. Learn more about your area of research & refine the scope.
Avoid Bias. Be aware of bias that you (as a researcher) may have.
Document your research. Use Google Docs to track your research process.
Research apps. Consider using Evernote or Zotero to track your research.

Consider Purpose

What will your topic and research address?

In The Literature Review: A Step-by-Step Guide for Students , Ridley presents that literature reviews serve several purposes (2008, p. 16-17). Included are the following points:

Historical background for the research;
Overview of current field provided by "contemporary debates, issues, and questions;"
Theories and concepts related to your research;
Introduce "relevant terminology" - or academic language - being used it the field;
Connect to existing research - does your work "extend or challenge [this] or address a gap;"
Provide "supporting evidence for a practical problem or issue" that your research addresses.

★ Schedule a research appointment

At this point in your literature review, take time to meet with a librarian. Why? Understanding the subject terminology used in databases can be challenging. Archer Librarians can help you structure a search, preparing you for step two. How? Contact a librarian directly or use the online form to schedule an appointment. Details are provided in the adjacent Schedule an Appointment box.

2. Search the Literature

Collect & Select Data: Preview, select, and organize

Archer Library is your go-to resource for this step in your literature review process. The literature search will include books and ebooks, scholarly and practitioner journals, theses and dissertations, and indexes. You may also choose to include web sites, blogs, open access resources, and newspapers. This library guide provides access to resources needed to complete a literature review.

Books & eBooks: Archer Library & OhioLINK

Databases: scholarly & practitioner journals.

Review the Library Databases tab on this library guide, it provides links to recommended databases for Education & Psychology, Business, and General & Social Sciences.

Expand your journal search; a complete listing of available AU Library and OhioLINK databases is available on the Databases A to Z list . Search the database by subject, type, name, or do use the search box for a general title search. The A to Z list also includes open access resources and select internet sites.

Databases: Theses & Dissertations

Review the Library Databases tab on this guide, it includes Theses & Dissertation resources. AU library also has AU student authored theses and dissertations available in print, search the library catalog for these titles.

Did you know? If you are looking for particular chapters within a dissertation that is not fully available online, it is possible to submit an ILL article request . Do this instead of requesting the entire dissertation.

Newspapers: Databases & Internet

Consider current literature in your academic field. AU Library's database collection includes The Chronicle of Higher Education and The Wall Street Journal . The Internet Resources tab in this guide provides links to newspapers and online journals such as Inside Higher Ed , COABE Journal , and Education Week .

Search Strategies & Boolean Operators

There are three basic boolean operators: AND, OR, and NOT.

Used with your search terms, boolean operators will either expand or limit results. What purpose do they serve? They help to define the relationship between your search terms. For example, using the operator AND will combine the terms expanding the search. When searching some databases, and Google, the operator AND may be implied.

Overview of boolean terms

About the example: Boolean searches were conducted on November 4, 2019; result numbers may vary at a later date. No additional database limiters were set to further narrow search returns.

Database Search Limiters

Database strategies for targeted search results.

Most databases include limiters, or additional parameters, you may use to strategically focus search results. EBSCO databases, such as Education Research Complete & Academic Search Complete provide options to:

Limit results to full text;
Limit results to scholarly journals, and reference available;
Select results source type to journals, magazines, conference papers, reviews, and newspapers
Publication date

Keep in mind that these tools are defined as limiters for a reason; adding them to a search will limit the number of results returned. This can be a double-edged sword. How?

If limiting results to full-text only, you may miss an important piece of research that could change the direction of your research. Interlibrary loan is available to students, free of charge. Request articles that are not available in full-text; they will be sent to you via email.
If narrowing publication date, you may eliminate significant historical - or recent - research conducted on your topic.
Limiting resource type to a specific type of material may cause bias in the research results.

Use limiters with care. When starting a search, consider opting out of limiters until the initial literature screening is complete. The second or third time through your research may be the ideal time to focus on specific time periods or material (scholarly vs newspaper).

★ Truncating Search Terms

Expanding your search term at the root.

Truncating is often referred to as 'wildcard' searching. Databases may have their own specific wildcard elements however, the most commonly used are the asterisk (*) or question mark (?). When used within your search. they will expand returned results.

Asterisk (*) Wildcard

Using the asterisk wildcard will return varied spellings of the truncated word. In the following example, the search term education was truncated after the letter "t."

Explore these database help pages for additional information on crafting search terms.

EBSCO Connect: Basic Searching with EBSCO
EBSCO Connect: Searching with Boolean Operators
EBSCO Connect: Searching with Wildcards and Truncation Symbols
ProQuest Help: Search Tips
ERIC: How does ERIC search work?

★ EBSCO Databases & Google Drive

Tips for saving research directly to Google drive.

Researching in an EBSCO database?

It is possible to save articles (PDF and HTML) and abstracts in EBSCOhost databases directly to Google drive. Select the Google Drive icon, authenticate using a Google account, and an EBSCO folder will be created in your account. This is a great option for managing your research. If documenting your research in a Google Doc, consider linking the information to actual articles saved in drive.

EBSCO Databases & Google Drive

EBSCOHost Databases & Google Drive: Managing your Research

This video features an overview of how to use Google Drive with EBSCO databases to help manage your research. It presents information for connecting an active Google account to EBSCO and steps needed to provide permission for EBSCO to manage a folder in Drive.

About the Video: Closed captioning is available, select CC from the video menu. If you need to review a specific area on the video, view on YouTube and expand the video description for access to topic time stamps. A video transcript is provided below.

EBSCOhost Databases & Google Scholar

Defining Literature Review

What is a literature review.

A definition from the Online Dictionary for Library and Information Sciences .

A literature review is "a comprehensive survey of the works published in a particular field of study or line of research, usually over a specific period of time, in the form of an in-depth, critical bibliographic essay or annotated list in which attention is drawn to the most significant works" (Reitz, 2014).

A systemic review is "a literature review focused on a specific research question, which uses explicit methods to minimize bias in the identification, appraisal, selection, and synthesis of all the high-quality evidence pertinent to the question" (Reitz, 2014).

About this page

EBSCO Connect [Discovery and Search]. (2022). Searching with boolean operators. Retrieved May, 3, 2022 from https://connect.ebsco.com/s/?language=en_US

EBSCO Connect [Discover and Search]. (2022). Searching with wildcards and truncation symbols. Retrieved May 3, 2022; https://connect.ebsco.com/s/?language=en_US

Machi, L.A. & McEvoy, B.T. (2009). The literature review . Thousand Oaks, CA: Corwin Press:

Reitz, J.M. (2014). Online dictionary for library and information science. ABC-CLIO, Libraries Unlimited . Retrieved from https://www.abc-clio.com/ODLIS/odlis_A.aspx

Ridley, D. (2008). The literature review: A step-by-step guide for students . Thousand Oaks, CA: Sage Publications, Inc.

Archer Librarians

Schedule an appointment.

Contact a librarian directly (email), or submit a request form. If you have worked with someone before, you can request them on the form.

★ Archer Library Help • Online Reqest Form
Carrie Halquist • Reference & Instruction
Jessica Byers • Reference & Curation
Don Reams • Corrections Education & Reference
Diane Schrecker • Education & Head of the IRC
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Sarah Thomas • Acquisitions & ATS Librarian
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Next: Literature Review Resources >>
Last Updated: Apr 23, 2024 3:36 PM
URL: https://libguides.ashland.edu/quantitative

Literature reviews

Introduction
Conducting your search
Store and organise the literature

Evaluate the information you have found

Critique the literature.

Different subject areas
Find literature reviews

When conducting your searches you may find many references that will not be suitable to use in your literature review.

Skim through the resource - a quick read through the table of contents, the introductory paragraph or the abstract should indicate whether you need to read further or whether you can immediately discard the result.
Evaluate the quality and reliability of the references you find - our page on evaluating information outlines what you need to consider when evaluating the books, journal articles, news and websites you find to ensure they are suitable for use in your literature review.

Critiquing the literature involves looking at the strength and weaknesses of the paper and evaluating the statements made by the author/s.

Books and resources on reading critically

CASP Checklists Critical appraisal tools designed to be used when reading research. Includes tools for Qualitative studies, Systematic Reviews, Randomised Controlled Trials, Cohort Studies, Case Control Studies, Economic Evaluations, Diagnostic Studies and Clinical Prediction Rule.
How to read critically - business and management From Postgraduate research in business - the aim of this chapter is to show you how to become a critical reader of typical academic literature in business and management.
Learning to read critically in language and literacy Aims to develop skills of critical analysis and research design. It presents a series of examples of `best practice' in language and literacy education research.
Critical appraisal in health sciences See tools for critically appraising health science research.

<< Previous: Store and organise the literature
Next: Different subject areas >>
Last Updated: Dec 15, 2023 12:09 PM
URL: https://guides.library.uq.edu.au/research-techniques/literature-reviews

Graduate Nursing

Electronic Resources
Finding Books
Professional Organizations
CRAAP Method
APA Guide 7th Edition

Literature Review

How to Search

Need more articles, but can't seem to find the right ones? Try these techniques!

Backwards searching: Once you find a relevant article, check the reference list at the end of the article. This will help you find other pertinent articles.

Forward searching : Once you find a relevant article, look at whether it has been cited in more-recent research. If a researcher cited it, it is likely that their paper will also relate to your topic. ResearchGate is a community for students and researchers. It lists where each of their publications have been cited, if at all. This can be found under the "citations" tab that pops up when you click on any publication.

When stuck, ask yourself, "What else is related to my topic?"

Get creative! You might find useful literature that you did not initially anticipate.

Fonseca, M. (2013, November 4) 5 tips to write a great literature review. https://www.editage.com/insights/5-tips-to-write-a-great-literature-review?refer=scroll-to-1-article&refer-type=article

What is a Literature Review?

"A literature review is a critical summary of all the published works on a particular topic" (Fonseca, 2013). A literature review provides background for your paper by quickly bringing the reader up-to-date on relevant findings, controversies, and dilemmas. It is the author's chance to "set the scene" and demonstrate why their topic is of interest to academia. In your literature review, you will describe "where your project comes from and how it fits in with existing knowledge" (Lloyd, 2017-2018). Further, you will provide "an argument for why your project makes a valuable contribution" (Lloyd, 2017-2018).

References:

Lloyd, C.(2017-2018). Literature reviews for sociology senior theses . [PowerPoint Slides]. https://socthesis.fas.harvard.edu/files/socseniorthesis/files/pres-litreview.pdf

Step One: Define Your Research Question

What are you trying to determine for your literature review? What specifically do you want to learn more about? Choose a topic that you are genuinely interested in. Next, conduct a broad search on it. Determine what trending and popular research is available, then narrow your topic down. You can refine it by one or more of the following:

Geographic location
Time period
Discipline/field of study, etc.

Research terms will help define your question.

A broad question might be something like: What is the homeless population like?
A narrow and specific question may include: What social and political factors have affected the growth of the middle-aged homeless population in Toronto within the past five years?

Once you have determined an appropriate research question/topic, move on to planning your approach.

Dermody, K., Literature Reviews. (2020, January 23). Retrieved from https://learn.library.ryerson.ca/literaturereview.

Step Two: Plan Your Approach

After you have landed a research question, ask yourself "Which specific terms will I use, and where am I going to begin?" Determine what kind of literature you want to look at, whether it be journal articles, books, electronic resources, newspapers, or even other literature reviews on similar topics.

Your keywords are the main concepts or ideas of your paper. For example, the keywords for a paper on “youth employment in Canada” would be:

Use synonyms: Often there are multiple ways to express the same concept. Make sure to use synonyms in your research. For instance, "employment" can be researched as:

Lastly, use “ AND ” and “ OR .” By bridging your truncated keywords and synonyms with the capitalized search words “AND” and “OR” (known as Boolean operators), you can search for multiple concepts effectively. For more information, visit the "electronic resources" tab of this research guide. There is a box on Boolean operators.

Step Four: Analyze Material

When searching for material, it is important to analyze your sources for credibility, accuracy, currency, and authenticity. Ask these questions when analyzing a source:

What is the purpose of the work?
How current is it?
Who is the author?
What are the author's biases?
Is this work peer reviewed?
How accurate is this information? What facts/empirical evidence support it?
What time frame are you looking at for your literature review, and does the work fall within that range?

Step Five: Manage Your Results

After analyzing your research and determining what sources you want to use, it's important to keep track of what you have looked through. Keep a list of the following:

What searches you have completed.
Which ones were successful and unsuccessful.
What databases you used.
What sources you want to use for your literature review.
What else you may want to search for next.

You can do this using software such as Zotero , Mendeley , and EndNote .

Congratulations! You are making progress towards an exceptional literature review.

Literature Review vs. Annotated Bibliography Both a literature review (A.K.A. literature synthesis) and an annotated bibliography summarize the existing body of knowledge on a given topic.

What is the difference between a literature review and an annotated bibliography? Unlike literature reviews, annotated bibliographies summarize entire research articles. An annotated bibliography looks like this:

Annotated Bibliography

• Summarizes each article separately.

o First, students discuss article one, then two, etc. o Topic: Blood Donation

Paragraph 1: Bonnie and Clyde (2019) wrote "this" on blood donation.
Paragraph 2: Rose and Jack (1997) wrote "this" on blood donation.
Paragraph 3: Mary-Kate and Ashley (2001) wrote "this" on blood donation.
Result: Multiple summaries of individual research articles (Lloyd, 2017-2018).

• Describes the existing body of knowledge by integrating and synthesizing the literature to create something new.

o Topic: Blood Donation

Paragraph 1: Information/research findings on red blood cells pulled from multiple sources.
Paragraph 2: Information/research findings on platelets pulled from multiple sources.
Paragraph 3: Information/research findings on white blood cells pulled from multiple sources.
Paragraph 4: Information/research findings on the drawbacks of donating blood from multiple sources (Lloyd, 2017-2018).
Result: The author points out "themes, concepts, gaps and disagreements" between articles (Hofer, Hanick & Townsend, 2019, p. 216). Students use these to describe the existing body of knowledge on their topic one concept at a time.

References:

Hofer, A. R., Hanick S. L., & Townsend, L. (2019). Designing activities for conceptual teaching. Transforming information literacy instruction: Threshold concepts in theory and practice. (p. 209-224). Libraries Unlimited.

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Not every source you found should be included in your annotated bibliography or lit review. Only include the most relevant and most important sources.

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Lit Review Prep Use this template to help you evaluate your sources, create article summaries for an annotated bibliography, and a synthesis matrix for your lit review outline.

Summarize your Sources

Summarize each source: Determine the most important and relevant information from each source, such as the findings, methodology, theories, etc. Consider using an article summary, or study summary to help you organize and summarize your sources.

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The library's tutorials about plagiarism are excellent, and will help you with paraphasing correctly

Annotated Bibliographies

Annotated bibliographies can help you clearly see and understand the research before diving into organizing and writing your literature review. Although typically part of the "summarize" step of the literature review, annotations should not merely be summaries of each article - instead, they should be critical evaluations of the source, and help determine a source's usefulness for your lit review.

Definition:

A list of citations on a particular topic followed by an evaluation of the source’s argument and other relevant material including its intended audience, sources of evidence, and methodology

Explore your topic.
Appraise issues or factors associated with your professional practice and research topic.
Help you get started with the literature review.
Think critically about your topic, and the literature.

Steps to Creating an Annotated Bibliography:

Find Your Sources
Read Your Sources
Identify the Most Relevant Sources
Cite your Sources
Write Annotations

Annotated Bibliography Resources

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Reference management is when you use specific tools to help you organize the references you find during a lit review search. On this page, we will present some video tutorials to get you started, a comparison chart of features from some popular reference managers, and questions to help you decide which one will work for you.

You can find more information on each reference management tool at the VCU Libraries Citation Tools guide.

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The Purpose of a Literature Review is to gain an understanding of the existing research relevant to a particular topic or area of study and to present that knowledge in the form of a written report. Learning important concepts, and research methods will bring insights into the topic chosen. Ultimately, achieving a better understanding of a particular discipline and/or topic based upon the research findings.

Writing the Literature Review: Step-by-Step Tutorial for Graduate Students - David Taylor, University of Maryland, Collage Park

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Open Access

Peer-reviewed

Research Article

Vowel onset measures and their reliability, sensitivity and specificity: A systematic literature review

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Voice Research Laboratory/ Doctor Liang Voice Program, Discipline of Speech Pathology, Faculty of Medicine and Health, Sydney School of Health Sciences, The University of Sydney, Sydney, NSW, Australia

Roles Data curation, Formal analysis, Investigation, Writing – review & editing

Roles Data curation, Formal analysis, Writing – review & editing

Roles Data curation, Writing – review & editing

Affiliation Division of Phoniatrics and Paediatric Audiology at the Department of Otorhinolaryngology Head & Neck Surgery, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

Roles Data curation

Affiliations Division of Phoniatrics and Paediatric Audiology at the Department of Otorhinolaryngology Head & Neck Surgery, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany, Department of Computer Science, Chair of Computer Science 5, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Bavaria, Germany

Roles Conceptualization, Formal analysis, Investigation, Writing – review & editing

Antonia Margarita Chacon,
Duy Duong Nguyen,
John Holik,
Michael Döllinger,
Tomás Arias-Vergara,
Catherine Jeanette Madill

Published: May 2, 2024
https://doi.org/10.1371/journal.pone.0301786
Peer Review
Reader Comments

To systematically evaluate the evidence for the reliability, sensitivity and specificity of existing measures of vowel-initial voice onset.

A literature search was conducted across electronic databases for published studies (MEDLINE, EMBASE, Scopus, Web of Science, CINAHL, PubMed Central, IEEE Xplore) and grey literature (ProQuest for unpublished dissertations) measuring vowel onset. Eligibility criteria included research of any study design type or context focused on measuring human voice onset on an initial vowel. Two independent reviewers were involved at each stage of title and abstract screening, data extraction and analysis. Data extracted included measures used, their reliability, sensitivity and specificity. Risk of bias and certainty of evidence was assessed using GRADE as the data of interest was extracted.

The search retrieved 6,983 records. Titles and abstracts were screened against the inclusion criteria by two independent reviewers, with a third reviewer responsible for conflict resolution. Thirty-five papers were included in the review, which identified five categories of voice onset measurement: auditory perceptual, acoustic, aerodynamic, physiological and visual imaging. Reliability was explored in 14 papers with varied reliability ratings, while sensitivity was rarely assessed, and no assessment of specificity was conducted across any of the included records. Certainty of evidence ranged from very low to moderate with high variability in methodology and voice onset measures used.

Conclusions

A range of vowel-initial voice onset measurements have been applied throughout the literature, however, there is a lack of evidence regarding their sensitivity, specificity and reliability in the detection and discrimination of voice onset types. Heterogeneity in study populations and methods used preclude conclusions on the most valid measures. There is a clear need for standardisation of research methodology, and for future studies to examine the practicality of these measures in research and clinical settings.

Citation: Chacon AM, Nguyen DD, Holik J, Döllinger M, Arias-Vergara T, Madill CJ (2024) Vowel onset measures and their reliability, sensitivity and specificity: A systematic literature review. PLoS ONE 19(5): e0301786. https://doi.org/10.1371/journal.pone.0301786

Editor: Li-Hsin Ning, National Taiwan Normal University, TAIWAN

Received: August 29, 2023; Accepted: March 21, 2024; Published: May 2, 2024

Copyright: © 2024 Chacon et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: Contributions by MD were supported by Deutsche Forschungsgemeinschaft (DFG) under grant no. DO1247/8-2. Contributions by TA were supported by Deutsche Forschungsgemeinschaft (DFG) under grant no. SCHU3441/3-2. Contributions by AC, DN and JH were supported by the Doctor Liang Voice Program at The University of Sydney. The funders had no role in study design, data collection and analysis, decision to publish, nor preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Measures of voicing control provide critical insight into a myriad of voice diagnoses across the lifespan. Voice disorders are highly prevalent, with an estimated one in thirteen adults experiencing a voice disorder each year [ 1 ]. Early and accurate diagnosis are essential to optimise patients’ vocal health outcomes. Traditionally, voice assessment and the evaluation of voice rehabilitative outcomes have focused upon voice quality [ 2 , 3 ] and patient-reported outcomes [ 4 ] as measures of voice function and efficiency. This assessment proforma typically involves the collection of a patient’s case history information, acoustic voice assessment and auditory perceptual judgement of the patient’s voice quality. Ideally, these tasks are also supplemented by laryngostroboscopic and aerodynamic assessment [ 5 , 6 ]. Most current voice assessment methods prioritise steady-state phonation with little, if any focus placed upon the initiation of voicing. Voice onset predicts the voice function that follows and as such, has been increasingly suggested as an effective means of assessing one’s voice, providing predictive information about phonation type, facilitating voice disorder diagnosis and determining one’s response to treatment [ 7 – 10 ].

Voice onset refers to the span of time between the release of a sound and the onset of voicing and involves several physiological processes. The onset of voice begins with transglottal airflow from the lungs bypassing the larynx and the start of vocal fold adduction. Small-amplitude, irregular vibration occurs at the edges of the vocal folds bordering the open glottis. Following the first instance of medial vocal fold contact, the amplitude of these vibrations grows, and steady-state oscillations are established [ 11 , 12 ]. The various physiological components involved in the onset of voice introduce many different means of voice onset measurement. There is also the compounding issue of differing types of voice onset. These are most commonly referred to as soft, breathy and hard, which are discernible to varying degrees depending on the measurement used.

There are two types of voice onset; one occurs after the release of a stop consonant and the other involves vowel phonation without a preceding consonant. Measures of voice onset which focus on the interval between the initial burst of a stop consonant and the voicing onset of the following vowel, e.g., ‘Voice Onset Time’ (VOT) [ 13 ], have been studied widely across populations and health statuses for many decades. The seminal papers in the voice onset literature typically relate to these such contexts of voice onset [ 14 – 18 ], as do most papers within the voice onset literature [ 12 ], with definitions of vowel-initial voice onset often being less clear. The onset of voicing which occurs when a vowel follows a consonant (CV), versus vowel-initial contexts of voicing varies considerably from a measurement perspective. CV measurement requires the ability to detect and differentiate between a consonant and vowel sound before analysing the vowel onset production, while vowel-initial contexts involve detection and measurement from the very start of voicing. Vowel-initial voice onset measurement is more clinically relevant than the measurement of CV productions, as vowel production is one of the standardised tasks performed in voice assessment [ 19 – 21 ]. It also allows for an indication of a patient’s voice production without the articulatory influences which are present in consonant-initial contexts [ 22 ]. Furthermore, the classification of voice onset types has been based primarily on vowel-centric tasks, and not upon vocal productions commencing with a consonant sound [ 7 , 23 ], and yet, vowel-initial voice onset has been researched to a lesser extent than CV voicing. As such, exploring the current state of the literature for specifically vowel-initial voicing onsets has been selected as a focus for this review.

The means through which voice onset has been measured across the existing evidence base is highly variable and has evolved with technological advances over time. Researchers measure voice onset through a range of measurement types, such as auditory perceptual measures, which involve making a judgement about the properties of a sound [ 23 – 25 ]; aerodynamic measures, such as phonatory airflow, volume and pressure [ 26 – 28 ]; physiologically, which monitors the physiological muscle movement associated with voice onset [ 11 , 29 , 30 ]; acoustically, which examines voice signal characteristics related to speech and voice production [ 12 , 31 , 32 ]; visually, through high-speed laryngoscopic examination of the vocal fold vibration associated with voice onset production [ 33 – 35 ], or through a combination of these [ 36 – 38 ]. Each of these methods of voice onset measurement present their own respective strengths and weaknesses, pertaining to the ability of each measure to reflect phonatory function or account for speaker variability, the reliability, sensitivity and specificity of the resulting measurement values, and factors associated with specific equipment requirements, training or skill-level in performing each measurement type. Nonetheless, no literature yet exists which has synthesised and consolidated the measures of voice onset which have been investigated, which are the most reliable, specific and sensitive in identifying or differentiating voice onset types, the contexts in which these measures may best be used, nor established a common language amongst voice onset types and the implications of these upon vocal function. It is imperative that these research gaps be filled so that valid clinical measures of voice onset can be established, which, in turn, can facilitate the inclusion of vowel onset measurement as part of the standardised clinical voice assessment proforma. The aim of this systematic review is to evaluate the evidence for sensitivity, specificity and reliability of vowel-initial voice onset measures, with the authors hypothesizing that high reliability, sensitivity and specificity ratings will indicate the most effective measures of vowel onset. To this end, the proposed systematic review will answer the following question: What are the methods of assessing vowel-initial voice onset and the evidence for their reliability, sensitivity and specificity?

Protocol and registration

This retrospective systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 39 ]. The protocol was registered through the PROSPERO International Prospective Register for Systematic Reviews (registration number CRD42021266384) and is provided in S1 File . The completed PRISMA 2020 checklist is provided in S1 Checklist .

Information sources

Databases searched were MEDLINE via OVID, EMBASE via OVID, Scopus, Web of Science, IEEE Xplore, CINAHL and PubMed Central. Grey literature was also searched through ProQuest to capture unpublished dissertations.

Search strategy

The initial search was conducted by AC in August 2021 and limited to articles published after January 1900. The search strategy was initially determined through discussions between four authors (AC, CM, MD, DN). The first author also conducted an updated search in December 2022 and May 2023 to capture any further articles of relevance ahead of publication.

The search string consisted of terms relating to three ‘concept areas’: voice onset, voice onset measures and evidence for measures of voice onset. Within the selected concept areas, we developed a list of synonyms and/or specific terms relevant to our search scope. The terms associated with each concept area were searched against the other concept word lists to achieve literature saturation of all relevant articles. The search strategies and Boolean operators applied to the MEDLINE, EMBASE, Scopus, Web of Science, IEEE Xplore, CINAHL, PubMed Central and ProQuest databases are provided in S2 File .

Inclusion criteria

The scope of this literature review was the onset of vowel phonation without a preceding consonant. Studies and unpublished works were included if they were written in English, related to measures of human voice onset and were published after 1900. Nil study design limits were enforced, nor were specific settings of interest; research occurring in both laboratory and clinical settings were included. Articles were excluded if they related to the onset of artificial or computerised tones, examined voice onset in vowels following the production of a consonant sound (i.e., Voice Onset Time) and/or were not written in the English language.

Study records

The database searches retrieved 6,983 records. These records were uploaded to the Covidence platform ( www.covidence.org ) to manage data, facilitate collaboration and document the review process over the course of the study.

Covidence identified 550 duplicates which were then removed for a total of 6,433 records. Titles and abstracts were screened against the inclusion criteria by two independent reviewers (any combination of MD, AC, DN, JH and TA). Any disagreements which arose between the reviewers at each stage of the selection process were resolved through the involvement of a third reviewer. Five thousand, nine hundred and twenty-two records were excluded based on titles and abstracts, with a further 11 studies being excluded as their papers could not be retrieved. Full texts of the remaining 500 records were assessed in detail against the inclusion criteria by two independent reviewers (any combination of DN, AC, MD, TA, JH and CM). Articles that did not meet the study criteria were removed, with reasons for exclusion being recorded. Four hundred and seventy-two papers were excluded from this process. For the purposes of literature saturation, a further hand search of the remaining articles’ citation lists was conducted (AC). Following a further process of title/abstract screening (MD, AC, DN, JH and TA), full text review and exclusion of inappropriate studies (AC, DN, MD, JH and TA), an additional seven studies were included.

An updated review of the literature was conducted in December 2022 and May 2023. The processes of title/abstract screening (AC, DN, JH), full text review and exclusion of inappropriate studies (AC, DN, JH), were again completed. The December 2022 search found nil further studies appropriate for inclusion, while the search conducted in May 2023 identified a further two studies. The final systematic review included 35 studies. A visual representation of this process is shown in Fig 1 , formatted according to the PRISMA 2020 statement [ 39 ].

PPT PowerPoint slide
PNG larger image
TIFF original image

https://doi.org/10.1371/journal.pone.0301786.g001

Data extraction and data items

Data was extracted from the included papers by all members of the research team. The data extraction process involved each team member reading the paper in its entirety, before extracting all information of relevance into the data extraction table. A simplified version of this table is presented in S3 File and the OSF Home Repository (DOI 10.17605/OSF.IO/N65SX ). Quantitative synthesis and meta-analyses were not completed owing to the heterogeneity of data and methodologies across studies. Rather, studies were grouped according to their voice onset measurement category (see Table 1 ). Following the study groupings, the data extracted from all studies across each measurement category was closely examined to identify key relationships and discrepancies across and between papers and categories. This informed the key research findings which are summarised in the Results section.

https://doi.org/10.1371/journal.pone.0301786.t001

Evaluation of certainty of evidence and risk of bias

The certainty of the included evidence was assessed through the Grading of Recommendations Assessment, Development and Evaluation (GRADE) working group methodology [ 40 ]. This involved each reviewer examining the quality of evidence through the domains of risk of bias, consistency, precision, directness and publication bias. This was particularly facilitated using the GRADE Handbook [ 41 ], which was used by team members to inform their assessment and provide a consistent evaluation across raters. Following this evaluation, it was determined whether the quality of the research could be deemed as high (i.e. very unlikely that further research will change our confidence in the estimate of effect), moderate (i.e. likely that further research will have an impact on our confidence in the estimate of effect and may change the estimate), low (i.e. very likely that further research will have an important impact on our confidence in the estimate of effect and is likely to change the estimate), or very low (i.e. very uncertain about the estimate of effect). The GRADEpro app was used to facilitate this process and ensure that the abovementioned terms were informed by a consistent, systematic process [ 42 – 44 ].

Process of identifying studies

The PRISMA flowchart in Fig 1 outlines the processes undertaken to collect and review the study records. Thirty-five records were identified as meeting the inclusion criteria for the review. Twenty-three studies involved visual imaging, 19 studies conducted acoustic analysis, 11 used physiological measures, seven studies involved auditory perceptual analysis, and four included aerodynamic analysis.

Study design

Of the 35 studies included, 26 used a cross-sectional design, six were validation studies, two were review papers with single or multiple case examples and one was a cohort study. No study used a randomised controlled trial design.

Study population characteristics

Table 1 presents an overview of each record included in the review, summarising study setting, participant characteristics, category of measurement and evidence certainty. It should be noted that while some studies specified the setting in which their research took place, most settings could only be extrapolated from the study methodology. Studies which used data from only vocally healthy, normophonic speakers (i.e., non-patients) were classified as taking place in a laboratory setting. Studies which involved patients with some form of voice disorder diagnosis were classified as ’clinical’. However, only one study explicitly stated that patients were recruited directly from a voice clinical setting [ 34 ]. Table 2 offers a summary of study population characteristics across the collective paper set, including sample size, age, gender, vocal health status and setting.

https://doi.org/10.1371/journal.pone.0301786.t002

Voice onset types

A definition of voice onset was provided in 25 of the 35 studies (see S1 Checklist ). Ten of these provided definitions of the specific voice onset measures used throughout the study (e.g., Vocal Attack Time), and 15 included the concept of voice onset being the period between the first adductory movement of the vocal folds and steady-state vibration. Twenty-one studies specifically examined different types of voice onset, namely being breathy (also referred to as ‘aspirate’), normal (also referred to as ‘comfortable’, ‘soft’, ‘easy’ and ‘modal’) and hard (also referred to as ‘glottal’, ‘pressed’ and ‘hard/glottal attack’) voice onset types.

Whilst these are auditory perceptual classifications, not all studies compared or validated their instrumental measures with independently-rated auditory perceptual judgements, despite using voice onset type as a classification or identifier. Only three studies of the review set compared their instrumental measure to perceptual judgements. As auditory perceptual judgement of voice is considered the ‘gold standard’ of voice assessment [ 61 ], it is noteworthy that few studies used comparisons to auditory perceptual judgements to validate the measure being investigated.

Across the 35 studies, a wide range of voice onset measures were explored. Amongst these, some focused on a singular measure (e.g., laryngeal reaction time) whilst others examined one measure using several means of instrumentation, for example, Vocal Attack Time (VAT), which is measured using the vocal acoustic and glottographic signals. Other studies examined or compared several measures of voice onset. Overall, 39 different measures of voice onset were identified across the collective set. Our team mutually agreed that the best means of synthesising and presenting this heterogeneous data set was through grouping the studies according to their measurement approach. As such, the following categories of measurement were identified; acoustic, aerodynamic, auditory-perceptual analysis, physiological measures and visual imaging. In any case where a given study explored more than one category of measurement, it was included across all relevant categories. The collective findings across each of these measurement categories are outlined in the sections below.

Voice onset measures

In total, there were 39 voice onset measures across the collective dataset. These are presented with their definitions in Table 3 . These measures were developed and investigated using different methods of analysis, which are described in the following text.

https://doi.org/10.1371/journal.pone.0301786.t003

Categories of voice onset measurement

A) auditory perceptual analysis..

Auditory perceptual analysis involves a listener making an auditory judgement about the properties of a sound. In the case of voice onset studies, this judgement often relates to the type of onset produced. Seven of the 35 included studies involved auditory-perceptual analysis. All seven studies involved perceptual ratings of phonation onset type, ranging from soft to hard [ 23 – 25 , 37 ], breathy to ‘German’ (a glottal plosive occurring in German classical singing) [ 36 ] and breathy to hard/ pressed [ 7 , 38 ]. For four of the seven studies [ 7 , 36 – 38 ], the auditory perceptual rating of samples was used only as a form of correlation to an instrumental measure of voice onset. This also served as confirmation that the participants had produced the onset types correctly before proceeding with other voice onset measurements; with 67% concordance between the attempted phonation type and rater in Shiba and Chhetri’s study, 68% agreement reported in Cooke et al.’s paper, 80% of samples being correctly identified in Freeman et al.’s study and 100% agreement on attack types in Koike’s study. Each of the studies explored different measures of voice onset, with three studies examining auditory perceptual judgements of voice onset as a voice onset measure in and of itself. Peters, Boves and Van Dielen, Maryn and Poncelet and Simon and Maryn’s papers focused on auditory perceptual judgement of voice onset as a standalone voice onset measure, with Maryn and Poncelet and Simon and Maryn concluding that there was considerable variability both between and within raters regarding the perception of voice onset type. Meanwhile, Peters reported moderately high reliability of ratings (r 1.1 = 0.74).

Automation of voice onset measurement was involved in four of the seven studies, and only in the processing and data generation stages for measures unrelated to auditory perceptual analysis. All seven studies performed some form of reliability analysis, which is presented in Table 4 . Two studies conducted both inter- and intra-rater reliability [ 24 , 25 ], with the remainder only exploring inter-rater reliability. Percentage agreement [ 7 , 36 – 38 ], product-moment correlations [ 23 ], the intraclass correlation coefficient [ 24 , 25 ] and Cohen’s kappa [ 25 ] were the statistical measures used to calculate reliability. None of the seven papers explored sensitivity nor specificity of data obtained.

https://doi.org/10.1371/journal.pone.0301786.t004

Collectively, the studies presented conflicting findings. Whilst Freeman et al., Peters et al. and Koike’s papers suggested listeners could discriminate well between onset types, Cooke et al., Shiba and Chhetri, Maryn and Poncelet and Simon and Maryn’s papers indicated that auditory perceptual judgement of voice onset type can be unreliable both within- and between-raters. Six of the studies reflect the lowest GRADE level of evidence with a rating of ‘very low’ evidence certainty and one with a rating of ‘low’ certainty of evidence. This low quality of research evidence combined with the variability in the findings of these studies calls into question the value of auditory perceptual judgements as the most accurate and reliable means of assessing voice onset in clinical contexts. A summary of data extracted from these auditory perceptual studies is provided in Table 5 .

https://doi.org/10.1371/journal.pone.0301786.t005

b) Acoustic analysis.

Acoustic analysis involves examining the recorded voice signal characteristics related to speech and voice production. Amongst the studies included, 19 utilised acoustic analysis in their voice onset measurement procedures. A wide range of acoustic voice onset measures were explored, as summarised in Table 6 , inclusive of Vocal Rise Time (VRT), the first peak of the acoustic derivative waveform (ADW1) and Laryngeal Reaction Time (LRT). Papers exploring most acoustically derived measures of voice onset did not typically provide numeric data for each onset type. Rather, these presented data ranging from descriptions of onset type differences, such as vibration and amplitude patterns, often in the absence of complete data reporting (for example, [ 30 ]), to small datasets regarding a new or uncommonly used voice onset measure. A common feature across all presented acoustic measures was the limited utility of applying these measures in clinical contexts, with many requiring specialised software or processes which would be expensive and/or impractical to complete during a clinical session.

https://doi.org/10.1371/journal.pone.0301786.t006

No specifications of voice recording equipment were provided for model number nor brand for six studies and two studies provided no specification whatsoever of device used. An integrated microphone (I.e., a microphone integrated into a stroboscopy or similar system) was used in two studies, and a further three studies used an audiotape recorder. Only one of the devices was used across more than one study (RadioShack 33–3012 head-mounted microphone), however all three studies in which it was used involved a similar research team. Some form of automation was involved in the methodology of 14 of the included acoustic analysis studies, and usually this was across both the processing and data generation stages using software platforms and mathematical algorithms. Three of the included papers used auditory perceptual analysis as a means of validating the instrumental measures used [ 36 – 38 ].

Only seven studies reported reliability assessment of acoustic analysis, of which two explored both inter- and intra-rater reliability [ 12 , 35 ] and five explored only inter-rater reliability [ 23 , 36 – 38 , 54 ]. The following statistical methods were used to determine reliability across the studies: Pearson product-moment correlation [ 12 , 23 , 51 , 54 – 56 ], percentage agreement [ 36 , 37 ] and multivariate tests [ 35 ]. One of the studies that used acoustic measurements for voice onset reported sensitivity analysis [ 35 ], with none conducting an analysis on specificity.

In summary, the included acoustic analysis studies reflected low evidence certainty, with outcomes from the GRADE Certainty Assessment yielding a ’very low’ rating for 14 studies, and a rating of ’low’ for the remaining five. While a large proportion of the reviewed studies involved acoustic analysis measures, there is evidently a vast range of acoustic analysis measures being used which prevents an in-depth understanding of any given measure. The acoustic analysis findings overall cannot be interpreted with high levels of confidence, nor are they of sufficient quality to inform the selection of the most reliable, sensitive, and specific acoustic voice onset measures for clinical practice.

c) Aerodynamic analysis.

Aerodynamic analysis refers to the measurement of phonatory airflow, volume, pressure and combined measures, such as efficiency and resistance. Four papers reported airflow measurement information informing some aspect of voice onset. The specific airflow measures explored across these studies included air consumption during the initial 200 milliseconds of different attack types (soft, breathy and hard) [ 37 ], Phonation Threshold Pressure (PTP) [ 27 ], Voice Onset Coordination (VOC) [ 28 ] and vocal onset according to transglottal airflow and intraglottal pressure [ 26 ].

Koike and LeBacq and DeJonckere’s papers similarly focused their studies upon exploring the characteristics of different voice onsets. Koike identified that soft and hard onsets were diametrically opposed across a range of measures, while the breathy onset showed little relation to either, having a ‘distinct character’ that differed completely from soft and hard onset types. LeBacq and DeJonckere namely used their airflow data as part of an intraglottal pressure calculation, while Madill et al.’s study correlated existing voice onset measures, including VOC, with the measure ADW1, concluding that it can be predicted from VOC. In Plant’s exploration of phonation threshold pressure, it was found that for most subjects, increasing airway resistance coincided with increasing threshold pressure.

Devices used for airflow measures were largely consistent, with three of the four studies using a Rothenberg mask or equivalent, and the other paper using a pneumatochograph [ 37 ]. Most of the four papers didn’t involve any automated processes, apart from Madill’s study, which involved some automation only in the data generation phase. Only Koike’s study involved some form of reliability assessment, being inter-rater reliability established through percentage agreement. None of the studies performed an analysis of sensitivity nor specificity. None of the included papers used auditory perceptual ratings to validate the instrumental measures of voice onset used.

Overall, the aerodynamic data presented across these four studies did not contribute significantly to an understanding of the most effective means of assessing voice onset through airflow. Other than Koike and Madill, there is a lack of transparency when it comes to presentation of the aerodynamic voice onset data. These findings should be considered as offering indefinite conclusions pertaining to the value of aerodynamic voice onset measurement, particularly as all four studies were graded as having the lowest certainty of evidence, being ‘very low’ evidence certainty according to the GRADE rating system. A summary of these aerodynamic analysis studies is provided in Table 7 .

https://doi.org/10.1371/journal.pone.0301786.t007

d) Physiological measures.

A range of other instrumental measures that monitor physiological muscle movement have been used to measure voice onset. For the purposes of this review, this specifically relates to electroglottography (EGG) and electromyography (EMG). EGG is a non-invasive technology used to measure the varying degrees of vocal fold contact during voice production, while EMG is a measure of muscular response or activation. Eleven studies explored physiological measures of voice onset. The specific types of voice onset measures examined in these studies included VAT [ 11 , 28 , 29 , 51 , 52 , 55 , 56 ], maximum of the first derivative of the EGG signal [ 27 ] and the interval between the first action potential (as detected by EMG) and the onset of sound [ 37 ].

The three studies of low evidence were largely conducted by the same research group [ 51 , 52 , 56 ], and all explored VAT as a measure of voice onset. However, the research questions posed in each of these studies differed, ranging from determining the fidelity of VAT as a voice onset measure to establishing normative VAT values. Pearson’s correlation coefficient was found to be a suitable fidelity metric (median correlation coefficient of 0.975 for 1033 VAT measures) [ 51 ], with the mean VAT among healthy young adults reported as 1.98ms. Aspirated voice onsets (e.g., the production of ‘hallways’) lead to a greater mean VAT than unaspirated voice onset tasks (e.g., the production of ‘always’) [ 56 ]. All remaining studies were of ‘very low’ evidence certainty; the majority of which also explored VAT.

Devices used across the physiological studies were varied, with three studies providing no specification of equipment. The remaining eight studies included one electromyograph and the remainder a combination of electroglottographs of different brands and models, with only the Glottal Enterprises EG2 and the KayPENTAX Fourcin Laryngograph model 6091 occurring in more than one study (each used in two studies). Six of the included studies involved automation as part of their study methodology for physiological measures, with five of these employing automated processes or algorithms across both the data processing and generation stages and one only using automation for data generation.

Reliability analysis was only performed in one study; Koike, 1967, which conducted inter-rater reliability as determined through percentage agreement (see Table 4 ). Neither sensitivity nor specificity analysis was conducted in any of the papers within this category. Only one of the papers in this set included auditory perceptual analysis to validate the instrumental measures of voice onset used.

Collectively, the studies of the highest GRADE level of evidence examining physiological measures of voice onset use VAT. Despite the greater breadth of research upon VAT than most other voice onset measures, there is a requirement to collect both electroglottographic and acoustic data to attain the VAT value. This, combined with the limited availability of the MATLAB-based program to calculate the measure, the heterogeneity amongst research questions posed in these studies, and the highest evidence rating according to the GRADE rating system as ‘low’ calls into question its clinical utility. A summary of the studies involving physiological analysis is provided in Table 8 .

https://doi.org/10.1371/journal.pone.0301786.t008

e) Visual imaging.

Visual imaging relates to any study whereby a measure of voice onset was based upon still or motion pictures of the larynx. Amongst the 35 included studies, 23 involved visual imaging in their measurement of voice onset. These studies investigated a range of measures related to voice onset, including Phonation Onset Time (POT) [ 38 , 48 , 50 , 59 ], measures of velocity, angle, distance and time associated with voice onset [ 7 ], Voice Initiation Period (VIP) [ 35 , 46 , 50 ] and Glottal Attack Time (GAT) [ 34 ].

Twenty of the 23 studies in this category involved high speed visual imaging, with kymography used in five studies [ 11 , 36 , 38 , 53 , 60 ], rigid laryngoscopy in one [ 7 ] and one employing cine-radiographic techniques, i.e., the recording of laryngeal movements on x-ray film [ 37 ]. Devices used across the visual imaging studies were varied, with the most common device used being the KayPENTAX colour high speed video system and component model 9710, used in five of the 23 studies. Six studies did not specify the device used, and of the remaining studies, 11 used some form of high-speed camera system and the remaining study performed cineradiography. Nineteen studies utilised a software program or mathematical algorithm to automate the processing and/or analysis of data pertaining to vocal fold vibration and glottal characteristics ( Table 9 ).

https://doi.org/10.1371/journal.pone.0301786.t009

Ten studies used reliability assessment in their measurement protocols, involving three which explored both inter- and intra-rater reliability [ 12 , 33 , 35 ], five inter-rater [ 7 , 34 , 36 – 38 ] and two intra-rater reliability assessments [ 49 , 50 ]. The statistical methods used for reliability assessment included Pearson product moment correlations [ 12 , 49 ], Cohen’s kappa [ 33 ], Cronbach alpha [ 50 ], Pearson’s correlation coefficient, general linear model and repeated measures analysis [ 35 ], the Wald 99% confidence interval [ 34 ] and percentage agreement [ 7 , 36 – 38 ]. Most studies did not report any sensitivity assessment, except for one paper [ 35 ]. No studies conducted specificity analysis. Three of the papers which involved visual imaging included auditory perceptual analysis to validate the instrumental measures of voice onset used.

Regarding the GRADE Certainty Assessment, one study was rated as ‘moderate’, two as ‘low’, and 20 as ’very low’ certainty of evidence. The findings of this section prove that the use of equipment (namely laryngoscopy) can introduce further variance in voice onset measures used, with an extensive range of voice onset measures despite the similarities across the visual imaging hardware used.

Automated voice onset measures

In examining the 35 studies, an interesting theme which arose was the increasing use of task automation to obtain voice onset measures in recent years. For the purposes of this review, ‘automation’ refers to any process throughout a study’s methodology which uses a form of computerised software or algorithm to eliminate the manual need to prepare or process data. Only nine studies [ 24 – 27 , 29 , 37 , 51 , 57 , 60 ] were found to involve no automated processes. These studies generally involved a research question focused upon auditory perceptual judgements, reliability or fidelity checking, or presented a descriptive review of a specific voice onset measure based on previous literature, and as such did not involve the analysis of large sets of objective voice onset measurement data. There were four studies which only involved automation in the pre-processing phase [ 23 , 33 , 34 , 38 ], with most using an automated process for both pre-processing and/or voice onset data output. Three studies used automation for data output alone [ 28 , 32 , 49 ]. According to measurement category, those studies which fell within the visual imaging and acoustic categories mainly used automation for processing and data. Across the remaining categories of physiological, aerodynamic and auditory perceptual studies, the automated phases of data analysis tended to vary more greatly.

Across the 26 studies which used automated algorithms, 12 used solely proprietary software or programs to perform automated functions upon their datasets, nine used only customised algorithms or programs, three used a combination of either proprietary and custom software, or used proprietary software with customised algorithms or applications specific to the research project and two were unspecified/unclear. There were several proprietary tools used across multiple studies, with the most common being MATLAB, in seven papers. While certain algorithms and filters were also named and described across studies, a close examination of these is beyond the scope of this paper.

Research quality

The process of data extraction included extracting data pertaining to the conduction of reliability, sensitivity or specificity analysis in any of the 35 studies. It was found that fourteen of the 35 studies conducted some form of reliability analysis while one conducted some form of sensitivity or specificity analysis. According to measurement category, reliability analysis was most commonly conducted in auditory perceptual studies, with all auditory perceptual papers conducting some form of reliability analysis. Reliability analysis was also common in the acoustic and visual imaging categories, with just under 50% of papers in both categories reporting reliability ratings. While 25% of papers in the aerodynamic category involved reliability analysis, this was least common in the physiologic category, with only one of 11 papers reporting reliability. Sensitivity was reported in one paper, which was common to both the acoustic and visual imaging categories. Specificity analysis was not conducted in any measurement category.

Of the papers which included reliability checking, two performed exclusively intra-rater reliability, while seven solely performed inter-rater reliability analysis. Five papers examined both intra- and inter-rater reliability. For intra-rater reliability, the number of samples re-rated for the purposes of reliability ranged from 10% [ 24 , 35 ] through to 36% [ 50 ], with reliability agreement ranging from an ICC value of 0.341 (one rater with poor intra-rater reliability [ 24 ]) to an ICC value of 0.975 [ 12 ]. Of those studies examining inter-rater reliability agreement, the number of samples re-rated varied from 10% [ 35 ] to 100% [ 7 , 23 – 25 , 36 – 38 ]. Inter-rater reliability agreement ranged from an ICC value of 0.145 [ 24 ] to 0.998 [ 54 ].

The metrics used to assess both intra- and inter-rater reliability included the intraclass correlation coefficient [ 23 – 25 ], Pearson product-moment correlations and absolute difference [ 12 , 49 ], Pearson’s correlation coefficient [ 35 , 54 ] and Cohen’s kappa [ 25 , 33 ]. Cronbach’s alpha [ 50 ] was used to determine intra-rater reliability in a single study, while percentage agreement [ 7 , 37 , 38 ], the general linear model and repeated measures of analysis [ 35 ] and the Wald 99% confidence interval [ 34 ] were used only for inter-rater reliability calculations. It should be noted that percentage agreement, as used in Shiba and Chhetri, Freeman et al., Cooke et al. and Koike’s studies should not be used as a standalone statistical measure for inter-rater reliability assessment, as these percentages do not account for concurrence that can be expected by chance, and ultimately does not represent a robust means of determining reliability agreement [ 25 ].

Only one of the 35 included studies conducted sensitivity analysis, with no studies conducting an analysis on specificity. Kunduk [ 35 ] posed a research question specifically related to sensitivity, determining whether the timing characteristics, pattern of adduction, start of vocal fold vibration and number of cycles required for the vocal folds to reach full vibration were sensitive to aging, as measured by the VIP. It found that timing characteristics during the VIP were sensitive to the effects of aging, with all timing variables being higher in the older group (mean age 76 years) than the younger group (mean age 26 years). However, the only measure found to reach a significant difference between the younger (mean = 11 cycles) and older groups (mean = 14 cycles) was the number of vocal fold oscillatory cycles before full length vocal fold vibration was achieved (p = 0.001). Across the remaining 34 studies, a select few made a comment relating to sensitivity when interpreting their results [ 30 , 37 , 47 , 54 , 55 ], however no sensitivity analyses was completed.

While most studies did not report sensitivity nor specificity analysis, 18 of the 35 did seek to use their chosen measure/s of voice onset to differentiate between voice onset types. However, many of these provided an in-text description of what appeared to differ across voice onset types (e.g., how a particular waveform or kymograph varied between breathy and hard onsets), rather than offering numerical cut-off values.

Overall, while the abovementioned papers report reliability outcomes to be of an acceptable level across studies, and VIP to be a sensitive measure of voice onset in detecting age-related differences between patients for the number of vocal fold oscillatory cycles, collectively it is clear that most voice onset measures have not been studied to the level required to be certain of their reliability, sensitivity and specificity.

GRADE evaluation of research quality

All authors used the GRADE system to evaluate research quality. This evaluation was completed immediately following data extraction for each study. Across all papers, the certainty of evidence as evaluated by GRADE ranged from ‘very low’ to ‘moderate’, with 27 of 35 papers falling in the ‘very low’ category, seven papers classed as ‘low’ certainty and one as ‘moderate’. GRADE certainty assessment values were similarly low across all measurement categories, with the single study assessed as moderate evidence certainty being classed within the ‘visual imaging’ category.

Acoustic analysis studies ranged from very low to low, with 14 categorised as ‘very low’ and five as ‘low’ certainty of evidence. Those four studies exploring aerodynamic analysis were all classed as ‘very low’ certainty of evidence, as was the case for six of the auditory perceptual papers, with one being classed as ‘low’ evidence certainty. The eleven physiological papers ranged from ‘very low’ to ‘low’ evidence certainty, with eight being ‘very low’ and three falling in the ‘low’ certainty of evidence category. Visual imaging was the voice onset measurement category with the largest number of papers, ranging from ‘very low’ to ‘moderate’ certainty of evidence. Amongst these papers, 19 were rated as ’very low’, three as ‘low’ and a single paper was deemed to have ‘moderate’ certainty of evidence.

Summary of main findings

Across the 35 studies included in this systematic review, all methods of voice onset measurement examined could be classified into one of five categories: auditory perceptual, acoustic, aerodynamic, physiological measures and visual imaging. These studies were evaluated as showing low level of evidence, ranging from very low to moderate certainty of evidence according to the GRADE rating system. Collectively, we found that the reviewed literature presents high variability in vowel onset measures, methodology and automated processes applied, with a lack of robust, high-quality data for any given measure of vowel onset. The voice onset measure explored by the greatest number of studies was VAT, having been examined in seven studies with the highest quality paper reflecting a GRADE rating of low-quality evidence. The paper with the highest evidence rating according to the GRADE system was of moderate evidence certainty [ 49 ], with all other papers being rated as low or very low. Overall, none of the 35 papers in question present high quality research evidence, with a clear paucity of studies examining measures of voice onset in a clinical context. As such, the present literature findings prevent a conclusion of which measures of voice onset would yield the most reliable results with satisfactory sensitivity and specificity to be used in clinical practice.

Heterogeneity in dataset

The collective data preclude a conclusion pertaining to the most reliable, sensitive and specific measures of voice onset for a variety of reasons. Firstly, across the 35 papers, there is great heterogeneity in the study populations used. There is variability in sample size, ranging from 1 to 112 participants per study and in ages explored, with those studies which report the age of their participants extending from ages eight to 87 years. A further source of variability is the genders included across the studies, with those which report the gender of their participants having an exclusively female or male population or a combination of both. Furthermore, the inclusion of a control or dysphonic group within each paper varies greatly. While most papers only examined normophonic participants, seven involved either an exclusively voice-disordered population or a matched group of participants with voice disorders, with diagnoses ranging from neurological disorders (spasmodic dysphonia) to vocal hyperfunction (vocal nodules) and malignant conditions (laryngeal cancer). Collectively, this extensive scope of participant demographics in each study population prevents both the generalisation of these findings to a larger population and the ability to draw an informed and cohesive conclusion pertaining to the reliability, sensitivity and specificity of the voice onset measures explored.

A further source of heterogeneity across the studies is found in the measurement methods used, with studies exploring either auditory perceptual, acoustic, aerodynamic, physiological or visual imaging-based measurement types, or in 18 studies, a combination of these. Across the 35 studies there are 39 different measures of voice onset used. Even in the case of VAT, the most explored voice onset measure in the dataset, there is variability in how this measure is collected, with a difference in approach evident across research groups. This variance in measurement methods over time can be attributed to technological advances. Many vowel-initial measures of voice onset may never reach the stage of becoming clinically practicable as new measures, based on updated technology and approaches, are constantly being developed before existing measures are sufficiently researched and applied to clinical contexts of voice assessment.

The automation of processes throughout the methodology of studies introduces a further source of variation in the voice onset literature. Automation is applied throughout the dataset in the stages of data processing, data generation or a combination of the two, with 27 of the 35 studies using automation in some capacity throughout their methodology. With a vast variety of algorithms and software platforms employed across these studies and the differing stages where these automated processes are applied, it is evident that automation introduces furthermore heterogeneity of measurement across the vowel-initial voice onset literature.

There are several potential sources of this heterogeneity. Voice onset is a complicated measure, such that currently there appears to be no single measure able to quantify it satisfactorily. This may have led to ‘exploratory’ studies in the absence of a theoretical model of voice onset, which introduces variation in the way vowel onset is measured and explored. Other sources can be attributed to the array of robust research indicators which are presently lacking across the vowel onset evidence base. The current evidence lacks well-designed studies which include a pre-calculated sample size, random sampling of the study population, theoretical models and reliability, sensitivity and specificity ratings for outcome measures of interest, reasonable rationales for vocal tasks used, voice disorder classification criteria, focal voice disorder populations (i.e., currently there are mixed population groups, such as functional and organic voice disorder types) and standardised voice onset measurement protocols. This range of factors can likely be attributed to the extensive variation between each of the studies which make up the collective set.

This heterogeneity in turn, limits interpretation and generalisability of the presented data. Across the study set, limited and underestimated sample sizes are highly prevalent, with all studies lacking a pre-calculated sample size with sufficient statistical power. This limits the ability to meaningfully interpret any data and apply this to larger populations. The lack of standardised protocols and reliability analyses across the reviewed studies is another contributing factor, which results in issues with the data reported and difficulty in interpreting this. Finally, the inconsistencies in methodology, outcome measures, measurement techniques and results across studies make it exceedingly difficult to draw significant trends and conclusions.

Collectively, there is great variability in the measurement of the voice onset phenomenon from methodological approach through to selected voice onset measure, leading to a vast array of data that can’t easily be replicated, interpreted nor synthesised. This heterogeneity prevents us from ascertaining the clinical utility of each respective measure and as such, disallows us from forming any generalisations pertaining to clinically valid measures of vowel onset. The diversity in methods and approaches highlights the lack of a commonly accepted standard when performing voice onset analysis, which further limits the opportunity to appreciate how voice onset could best, most reliably, sensitively and specifically be applied in a clinical context.

Voice onset definitions

An added limitation of the study findings is grounded in the lack of accepted definitions pertaining to voice onset in vowel-initial contexts. While most studies provided some form of voice onset definition, there was considerable variation between these; with ten defining only the specific voice onset measure/s examined in their study and a further ten papers describing voice onset according to a clear and detailed definition which accounted for the range of physiological processes involved. Of the papers which did not specify the meaning of voice onset, these often reported providing instruction, training and/or modelling to study participants which is not detailed in each paper (for example, [ 36 ]). Training of subjects requires perceptual judgement of voice onset by trainers and speakers to perform the voice onset. Therefore, the lack of independent verification of perceptual features present in the samples where auditory perceptual ratings were not used is problematic. This lack of reporting also limits the opportunity for replicability and consistency between studies. Without the provision of clear and explicit definitions of vowel-initial voice onset across the literature, it is difficult to establish if the phenomenon being measured is in fact voice onset. Given that the definition of voice onset informs the methodology and nature of research conducted across each study, this discrepancy across the collective dataset is a clear contributing factor to the heterogeneity of study design and outcomes.

The issue of ambiguity surrounding what specifically is being measured as voice onset is further compounded by the lack of correlation with auditory perceptual judgements throughout the collective group. With only three of the papers correlating their instrumental measures of voice onset with a perceptual judgement of onset type, most papers are neglecting the gold standard of voice assessment and in so doing, bringing into question the validity of their chosen measures of vowel-initial voice onset.

Quality of evidence

The GRADE findings of this review evidenced that the quality of papers throughout the vowel-initial voice onset literature is low, informed largely by the research design and small sample size of all studies examined. Amongst these papers there was a low incidence of reliability assessments to ascertain the reproducibility of research findings, with some form of reliability assessment occurring in only 14 of the 35 papers. Across these papers, these ratings tended to be quite variable, including instances of low reliability reported. This may have resulted from factors pertaining to the raters themselves (i.e., variation in clinical experience, skill set and training in use of the measurement tool) but is most likely attributable to elements associated with research quality, such as study design, sample size and sampling methods. A cross-sectional study is typically less reliable than prospective or cohort studies, small sample sizes yield less reliable results than studies involving greater participant numbers and convenience sampling is generally less reliable than random sampling. With cross-sectional studies being the most common study design and the use of small sample sizes attained through convenience sampling across the 35 papers, the overall low quality of the collective paper set elucidates some causative factors behind the low and variable reliability results reported in this review.

Compared to reliability analysis, even lower rates of sensitivity assessment were performed with only a single study reporting some form of sensitivity analysis, and nil studies were found to analyse specificity. Almost none of the reviewed studies used voice onset measures to discriminate disordered from non-disordered speakers. Furthermore, voice onset measures were not used as an outcome to detect participants’ vocal condition. These factors help to account for the lack of discrimination analyses conducted across the studies.

Strengths and limitations

The papers included in the systematic review covered all types of relevant literature available at the time of the study, featuring a comprehensive search strategy including both published papers and grey literature sources. Updated searches were conducted in December 2022 and May 2023 to ensure all recently published articles of interest were considered for review. Limitations of the study approach include only examining literature published in the English language i.e., excluding non-English sources, and not performing a further citation search of the two studies added to the dataset from the final updated literature search, which may have potentially sourced further studies of relevance. A lack of quantitative data and a high level of heterogeneity between the studies prevented the conduction of a quantitative analysis of the collective study findings. The dearth of data conducted beyond a laboratory-based setting also made it difficult to determine which measures of voice onset may be most practical for application in clinical contexts. As such, we are unable to develop well-informed recommendations and conclusions pertaining to how voice onset may be most effectively measured in patient scenarios, as these conclusions would not be supported by research we would describe as reliable, sensitive nor specific.

Comparison with other studies

Nil other review studies have been conducted into vowel-initial voice onset measurement to enable a direct comparison with the existing literature, however, several studies have recognised that the existing pool of voice onset measurement literature presents a heterogeneous set of data and low level of evidence methodologies. For example, Patel [ 49 ] reported that studies investigating the onset of phonation examine small cohorts of vocally healthy adults and have utilised different waveform types, which yields variable findings. Likewise, Petermann and colleagues [ 62 ] recognised that the present literature involves different approaches to measuring even the same voice onset measure, with no standardised processes in place and wide inter- and intrasubject variability, which complicates the cross-study comparison of results. Maryn and Poncelet [ 24 ] also recognised the failings of the existing voice onset literature in examining or developing a range of quantitative, objective voice onset measures, without any application to clinical voice assessment protocols nor patient-centric contexts.

Clinical implications

The lack of an accepted standard pertaining to vowel-initial voice onset measurement in clinical contexts is directly evidenced in the range of clinical voice assessment proformas which lack an assessment of this feature. Despite the utility of vowel-initial voice onset in providing predictive information pertaining to the voice function that follows, the plethora of studies relating to vowel-initial voice onset measures have proved trivial in bridging the gap between theory and practice; failing to identify a single form of measurement which is proven to yield reliable, sensitive and specific results which can be applied to clinical voice patient contexts. Until such a measurement tool can be identified and researched to prove its utility as a clinically valid measure, it seems that clinical voice assessment and the standardisation of voice assessment tasks will continue to be limited by the current gaps in the voice onset literature.

Implications for research and future studies

Further, high quality research is clearly needed in the vowel-initial voice onset measurement space, preferably, within the next five to ten years. These papers would ideally involve a comparison of voice onset measures using methods of assessment which could easily and efficiently be applied in clinical contexts, as well as validation of these individual measures. In addition, further research into standardised measurement criteria and voice assessment protocols which incorporate clinically viable measures of vowel initial voice onset would prove valuable. Given that vowel-initial voice onset measures provide useful information for all voice disorder populations, diverse populations and disorder types would need to be considered. Performing effect size calculations which are clearly documented in the resulting manuscript, and seeking large study populations wherever possible should be prioritised.

Further research should also perform independent auditory perceptual ratings of samples for cross-comparison; ideally using publicly available voice databases wherever possible. It is also of utmost importance that future voice onset research presents a physiological definition of what precisely each study will measure, rather than measuring voice onset solely according to perceptual judgements of voice onset type. In the same vein, these studies must also ensure that the measure they select is able to assess these physiological features, rather than base a measurement upon inference. The development of such research would lead to far greater confidence in the collective findings across the vowel-initial voice onset literature, and an ability to develop informed recommendations pertaining to the application of these measures in a clinical capacity.

Voice onset is a highly variable event involving multiple physiological processes and as such, is a difficult phenomenon to measure. The findings of this review do not permit us to provide informed recommendations regarding the most reliable, sensitive and specific means of measuring vowel-initial voice onset, due to the heterogeneity and overall low research quality of the examined studies. There is a clear need for high-quality data and well-designed research which examines voicing control across the lifespan and across disorders. Ideally, this should compare a range of measures, particularly those which would be easily practicable in clinical scenarios, and provide a robust evaluation of their reliability, sensitivity and specificity in patient-based contexts.

Supporting information

S1 checklist. prisma 2020 checklist..

https://doi.org/10.1371/journal.pone.0301786.s001

S1 File. Systematic review protocol.

https://doi.org/10.1371/journal.pone.0301786.s002

S2 File. Database search strategy.

https://doi.org/10.1371/journal.pone.0301786.s003

S3 File. Data extraction summary table.

https://doi.org/10.1371/journal.pone.0301786.s004

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Title: when llms meet cybersecurity: a systematic literature review.

Abstract: The rapid advancements in large language models (LLMs) have opened new avenues across various fields, including cybersecurity, which faces an ever-evolving threat landscape and need for innovative technologies. Despite initial explorations into the application of LLMs in cybersecurity, there is a lack of a comprehensive overview of this research area. This paper bridge this gap by providing a systematic literature review, encompassing an analysis of over 180 works, spanning across 25 LLMs and more than 10 downstream scenarios. Our comprehensive overview addresses three critical research questions: the construction of cybersecurity-oriented LLMs, LLMs' applications in various cybersecurity tasks, and the existing challenges and further research in this area. This study aims to shed light on the extensive potential of LLMs in enhancing cybersecurity practices, and serve as a valuable resource for applying LLMs in this doamin. We also maintain and regularly updated list of practical guides on LLMs for cybersecurity at this https URL .

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Literature Reviews. Summarize existing printed or electronic information on a specific subject in a literature review. A literature review may be a self-contained document, or it may be a section of a larger report . Determine the amount, scope and density of information to be included in your review by assessing your audience's purpose and ...
Evaluate and critique the literature
When conducting your searches you may find many references that will not be suitable to use in your literature review. Skim through the resource - a quick read through the table of contents, the introductory paragraph or the abstract should indicate whether you need to read further or whether you can immediately discard the result.
Research Guides: Graduate Nursing : Literature Review
Literature Review. • Describes the existing body of knowledge by integrating and synthesizing the literature to create something new. o Topic: Blood Donation. Paragraph 1: Information/research findings on red blood cells pulled from multiple sources. Paragraph 2: Information/research findings on platelets pulled from multiple sources.
Summarize
Annotated Bibliographies. Annotated bibliographies can help you clearly see and understand the research before diving into organizing and writing your literature review. Although typically part of the "summarize" step of the literature review, annotations should not merely be summaries of each article - instead, they should be critical ...
Reference Management
Reference management is when you use specific tools to help you organize the references you find during a lit review search. On this page, we will present some video tutorials to get you started, a comparison chart of features from some popular reference managers, and questions to help you decide which one will work for you.
Publications
A literature review is an evaluation of existing research works on a specific academic topic, theme or subject to identify gaps and propose future research agenda. ... which is to obtain a representative number of appropriate references for conducting a thorough literature review. Whether a reference is appropriate will depend on the focus of ...
What is a Literature Review?
The Purpose of a Literature Review is to gain an understanding of the existing research relevant to a particular topic or area of study and to present that knowledge in the form of a written report. Learning important concepts, and research methods will bring insights into the topic chosen. Ultimately, achieving a better understanding of a particular discipline and/or topic based upon the ...
(Pdf) Literature Review in Research
references for life science and biomedical research. literature, covering peer-reviewed article abstracts ... A thorough, sophisticated literature review is the foundation and inspiration for ...
A Literature Review: Website Design and User Engagement
2.3. Analysis. The literature review uncovered 20 distinct design elements commonly discussed in research that affect user engagement. They were (1) organization - is the website logically organized, (2) content utility - is the information provided useful or interesting, (3) navigation - is the website easy to navigate, (4) graphical representation - does the website utilize icons ...
Vowel onset measures and their reliability, sensitivity and specificity
The scope of this literature review was the onset of vowel phonation without a preceding consonant. Studies and unpublished works were included if they were written in English, related to measures of human voice onset and were published after 1900. ... References. 1. Bhattacharyya N. The prevalence of voice problems among adults in the United ...
When LLMs Meet Cybersecurity: A Systematic Literature Review
The rapid advancements in large language models (LLMs) have opened new avenues across various fields, including cybersecurity, which faces an ever-evolving threat landscape and need for innovative technologies. Despite initial explorations into the application of LLMs in cybersecurity, there is a lack of a comprehensive overview of this research area. This paper bridge this gap by providing a ...
Successful surgical management of giant mucinous cystic ...
Successful surgical management of giant mucinous cystic neoplasm of liver (MCN-L) presenting with peritoneal rupture and biliary prolapse: Case report and review of literature. Author links open overlay panel Ruchi Rastogi a , Subhash Gupta b 1 , Sanjiv Saigal b 2 , Mukesh Kumar b 3 , Rohan Luthra a 4 , Riti Agarwal c 5 , Bharat Aggarwal a 6

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Researching and writing for Economics students

4.1 What is the point of a literature survey?

4.2 What previous work is relevant?

4.3 What are “good” economics journal articles?

Unpublished “working papers”

4.4 How to find and access articles

4.5 Good starting points: Survey article, course notes, and textbooks

4.6 Backwards and forwards with references

4.7 Citations

List of works cited

Avoiding plagiarism and academic offenses**

4.8 How to write about previous authors’ analysis and findings

“Findings”: Critically examine sources

“Findings:” “They Proved”

“Findings”: How do you (or the cited paper) claim to identify a causal relationship?

4.9 …Stating empirical results

4.10 What to report

4.11 Organising your literature review

4.12 What if you have trouble reading and understanding a paper?

4.13 Some literature survey do’s and don’ts

4.14 Comprehension questions: literature review

Literature Reviews

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Literature Reviews by Lawrence A. Machi , Brenda T. McEvoy LAST REVIEWED: 27 October 2016 LAST MODIFIED: 27 October 2016 DOI: 10.1093/obo/9780199756810-0169

Literature Review - what is a Literature Review, why it is important and how it is done

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