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Evidence – Definition, Types and Example

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Definition:

Evidence is any information or data that supports or refutes a claim, hypothesis, or argument. It is the basis for making decisions, drawing conclusions, and establishing the truth or validity of a statement.

Types of Evidence

Types of Evidence are as follows:

Empirical evidence

This type of evidence comes from direct observation or measurement, and is usually based on data collected through scientific or other systematic methods.

Expert Testimony

This is evidence provided by individuals who have specialized knowledge or expertise in a particular area, and can provide insight into the validity or reliability of a claim.

Personal Experience

This type of evidence comes from firsthand accounts of events or situations, and can be useful in providing context or a sense of perspective.

Statistical Evidence

This type of evidence involves the use of numbers and data to support a claim, and can include things like surveys, polls, and other types of quantitative analysis.

Analogical Evidence

This involves making comparisons between similar situations or cases, and can be used to draw conclusions about the validity or applicability of a claim.

Documentary Evidence

This includes written or recorded materials, such as contracts, emails, or other types of documents, that can provide support for a claim.

Circumstantial Evidence

This type of evidence involves drawing inferences based on indirect or circumstantial evidence, and can be used to support a claim when direct evidence is not available.

Examples of Evidence

Here are some examples of different types of evidence that could be used to support a claim or argument:

• A study conducted on a new drug, showing its effectiveness in treating a particular disease, based on clinical trials and medical data.
• A doctor providing testimony in court about a patient’s medical condition or injuries.
• A patient sharing their personal experience with a particular medical treatment or therapy.
• A study showing that a particular type of cancer is more common in certain demographics or geographic areas.
• Comparing the benefits of a healthy diet and exercise to maintaining a car with regular oil changes and maintenance.
• A contract showing that two parties agreed to a particular set of terms and conditions.
• The presence of a suspect’s DNA at the crime scene can be used as circumstantial evidence to suggest their involvement in the crime.

Applications of Evidence

Here are some applications of evidence:

• Law : In the legal system, evidence is used to establish facts and to prove or disprove a case. Lawyers use different types of evidence, such as witness testimony, physical evidence, and documentary evidence, to present their arguments and persuade judges and juries.
• Science : Evidence is the foundation of scientific inquiry. Scientists use evidence to support or refute hypotheses and theories, and to advance knowledge in their fields. The scientific method relies on evidence-based observations, experiments, and data analysis.
• Medicine : Evidence-based medicine (EBM) is a medical approach that emphasizes the use of scientific evidence to inform clinical decision-making. EBM relies on clinical trials, systematic reviews, and meta-analyses to determine the best treatments for patients.
• Public policy : Evidence is crucial in informing public policy decisions. Policymakers rely on research studies, evaluations, and other forms of evidence to develop and implement policies that are effective, efficient, and equitable.
• Business : Evidence-based decision-making is becoming increasingly important in the business world. Companies use data analytics, market research, and other forms of evidence to make strategic decisions, evaluate performance, and optimize operations.

Purpose of Evidence

The purpose of evidence is to support or prove a claim or argument. Evidence can take many forms, including statistics, examples, anecdotes, expert opinions, and research studies. The use of evidence is important in fields such as science, law, and journalism to ensure that claims are backed up by factual information and to make decisions based on reliable information. Evidence can also be used to challenge or question existing beliefs and assumptions, and to uncover new knowledge and insights. Overall, the purpose of evidence is to provide a foundation for understanding and decision-making that is grounded in empirical facts and data.

Characteristics of Evidence

Some Characteristics of Evidence are as follows:

• Relevance : Evidence must be relevant to the claim or argument it is intended to support. It should directly address the issue at hand and not be tangential or unrelated.
• Reliability : Evidence should come from a trustworthy and reliable source. The credibility of the source should be established, and the information should be accurate and free from bias.
• Sufficiency : Evidence should be sufficient to support the claim or argument. It should provide enough information to make a strong case, but not be overly repetitive or redundant.
• Validity : Evidence should be based on sound reasoning and logic. It should be based on established principles or theories, and should be consistent with other evidence and observations.
• Timeliness : Evidence should be current and up-to-date. It should reflect the most recent developments or research in the field.
• Accessibility : Evidence should be easily accessible to others who may want to review or evaluate it. It should be clear and easy to understand, and should be presented in a way that is appropriate for the intended audience.

Advantages of Evidence

The use of evidence has several advantages, including:

• Supports informed decision-making: Evidence-based decision-making enables individuals or organizations to make informed choices based on reliable information rather than assumptions or opinions.
• Enhances credibility: The use of evidence can enhance the credibility of claims or arguments by providing factual support.
• Promotes transparency: The use of evidence promotes transparency in decision-making processes by providing a clear and objective basis for decisions.
• Facilitates evaluation : Evidence-based decision-making enables the evaluation of the effectiveness of policies, programs, and interventions.
• Provides insights: The use of evidence can provide new insights and perspectives on complex issues, enabling individuals or organizations to approach problems from different angles.
• Enhances problem-solving : Evidence-based decision-making can help individuals or organizations to identify the root causes of problems and develop more effective solutions.

Limitations of Evidence

Some Limitations of Evidence are as follows:

• Limited availability : Evidence may not always be available or accessible, particularly in areas where research is limited or where data collection is difficult.
• Interpretation challenges: Evidence can be open to interpretation, and individuals may interpret the same evidence differently based on their biases, experiences, or values.
• Time-consuming: Gathering and evaluating evidence can be time-consuming and require significant resources, which may not always be feasible in certain contexts.
• May not apply universally : Evidence may be context-specific and may not apply universally to other situations or populations.
• Potential for bias: Even well-designed studies or research can be influenced by biases, such as selection bias, measurement bias, or publication bias.
• Ethical concerns : Evidence may raise ethical concerns, such as the use of personal data or the potential harm to research participants.

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Evidence-Based Research: Levels of Evidence Pyramid

Introduction.

One way to organize the different types of evidence involved in evidence-based practice research is the levels of evidence pyramid. The pyramid includes a variety of evidence types and levels.

• systematic reviews
• critically-appraised topics
• critically-appraised individual articles
• randomized controlled trials
• cohort studies
• case-controlled studies, case series, and case reports
• Background information, expert opinion

Levels of evidence pyramid

The levels of evidence pyramid provides a way to visualize both the quality of evidence and the amount of evidence available. For example, systematic reviews are at the top of the pyramid, meaning they are both the highest level of evidence and the least common. As you go down the pyramid, the amount of evidence will increase as the quality of the evidence decreases.

Text alternative for Levels of Evidence Pyramid diagram

EBM Pyramid and EBM Page Generator, copyright 2006 Trustees of Dartmouth College and Yale University. All Rights Reserved. Produced by Jan Glover, David Izzo, Karen Odato and Lei Wang.

Filtered Resources

Filtered resources appraise the quality of studies and often make recommendations for practice. The main types of filtered resources in evidence-based practice are:

Scroll down the page to the Systematic reviews , Critically-appraised topics , and Critically-appraised individual articles sections for links to resources where you can find each of these types of filtered information.

Systematic reviews

Authors of a systematic review ask a specific clinical question, perform a comprehensive literature review, eliminate the poorly done studies, and attempt to make practice recommendations based on the well-done studies. Systematic reviews include only experimental, or quantitative, studies, and often include only randomized controlled trials.

You can find systematic reviews in these filtered databases :

• Cochrane Database of Systematic Reviews Cochrane systematic reviews are considered the gold standard for systematic reviews. This database contains both systematic reviews and review protocols. To find only systematic reviews, select Cochrane Reviews in the Document Type box.
• JBI EBP Database (formerly Joanna Briggs Institute EBP Database) This database includes systematic reviews, evidence summaries, and best practice information sheets. To find only systematic reviews, click on Limits and then select Systematic Reviews in the Publication Types box. To see how to use the limit and find full text, please see our Joanna Briggs Institute Search Help page .

You can also find systematic reviews in this unfiltered database :

To learn more about finding systematic reviews, please see our guide:

• Filtered Resources: Systematic Reviews

Critically-appraised topics

Authors of critically-appraised topics evaluate and synthesize multiple research studies. Critically-appraised topics are like short systematic reviews focused on a particular topic.

You can find critically-appraised topics in these resources:

• Annual Reviews This collection offers comprehensive, timely collections of critical reviews written by leading scientists. To find reviews on your topic, use the search box in the upper-right corner.
• Guideline Central This free database offers quick-reference guideline summaries organized by a new non-profit initiative which will aim to fill the gap left by the sudden closure of AHRQ’s National Guideline Clearinghouse (NGC).
• JBI EBP Database (formerly Joanna Briggs Institute EBP Database) To find critically-appraised topics in JBI, click on Limits and then select Evidence Summaries from the Publication Types box. To see how to use the limit and find full text, please see our Joanna Briggs Institute Search Help page .
• National Institute for Health and Care Excellence (NICE) Evidence-based recommendations for health and care in England.
• Filtered Resources: Critically-Appraised Topics

Critically-appraised individual articles

Authors of critically-appraised individual articles evaluate and synopsize individual research studies.

You can find critically-appraised individual articles in these resources:

• EvidenceAlerts Quality articles from over 120 clinical journals are selected by research staff and then rated for clinical relevance and interest by an international group of physicians. Note: You must create a free account to search EvidenceAlerts.
• ACP Journal Club This journal publishes reviews of research on the care of adults and adolescents. You can either browse this journal or use the Search within this publication feature.
• Evidence-Based Nursing This journal reviews research studies that are relevant to best nursing practice. You can either browse individual issues or use the search box in the upper-right corner.

To learn more about finding critically-appraised individual articles, please see our guide:

• Filtered Resources: Critically-Appraised Individual Articles

Unfiltered resources

You may not always be able to find information on your topic in the filtered literature. When this happens, you'll need to search the primary or unfiltered literature. Keep in mind that with unfiltered resources, you take on the role of reviewing what you find to make sure it is valid and reliable.

Note: You can also find systematic reviews and other filtered resources in these unfiltered databases.

The Levels of Evidence Pyramid includes unfiltered study types in this order of evidence from higher to lower:

You can search for each of these types of evidence in the following databases:

TRIP database

Background information & expert opinion.

Background information and expert opinions are not necessarily backed by research studies. They include point-of-care resources, textbooks, conference proceedings, etc.

• Family Physicians Inquiries Network: Clinical Inquiries Provide the ideal answers to clinical questions using a structured search, critical appraisal, authoritative recommendations, clinical perspective, and rigorous peer review. Clinical Inquiries deliver best evidence for point-of-care use.
• Harrison, T. R., & Fauci, A. S. (2009). Harrison's Manual of Medicine . New York: McGraw-Hill Professional. Contains the clinical portions of Harrison's Principles of Internal Medicine .
• Lippincott manual of nursing practice (8th ed.). (2006). Philadelphia, PA: Lippincott Williams & Wilkins. Provides background information on clinical nursing practice.
• Medscape: Drugs & Diseases An open-access, point-of-care medical reference that includes clinical information from top physicians and pharmacists in the United States and worldwide.
• Virginia Henderson Global Nursing e-Repository An open-access repository that contains works by nurses and is sponsored by Sigma Theta Tau International, the Honor Society of Nursing. Note: This resource contains both expert opinion and evidence-based practice articles.
• Previous Page: Phrasing Research Questions
• Next Page: Evidence Types
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Levels of evidence in research

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Table of Contents

Level of evidence hierarchy

When carrying out a project you might have noticed that while searching for information, there seems to be different levels of credibility given to different types of scientific results. For example, it is not the same to use a systematic review or an expert opinion as a basis for an argument. It’s almost common sense that the first will demonstrate more accurate results than the latter, which ultimately derives from a personal opinion.

In the medical and health care area, for example, it is very important that professionals not only have access to information but also have instruments to determine which evidence is stronger and more trustworthy, building up the confidence to diagnose and treat their patients.

5 levels of evidence

With the increasing need from physicians – as well as scientists of different fields of study-, to know from which kind of research they can expect the best clinical evidence, experts decided to rank this evidence to help them identify the best sources of information to answer their questions. The criteria for ranking evidence is based on the design, methodology, validity and applicability of the different types of studies. The outcome is called “levels of evidence” or “levels of evidence hierarchy”. By organizing a well-defined hierarchy of evidence, academia experts were aiming to help scientists feel confident in using findings from high-ranked evidence in their own work or practice. For Physicians, whose daily activity depends on available clinical evidence to support decision-making, this really helps them to know which evidence to trust the most.

So, by now you know that research can be graded according to the evidential strength determined by different study designs. But how many grades are there? Which evidence should be high-ranked and low-ranked?

There are five levels of evidence in the hierarchy of evidence – being 1 (or in some cases A) for strong and high-quality evidence and 5 (or E) for evidence with effectiveness not established, as you can see in the pyramidal scheme below:

Level 1: (higher quality of evidence) – High-quality randomized trial or prospective study; testing of previously developed diagnostic criteria on consecutive patients; sensible costs and alternatives; values obtained from many studies with multiway sensitivity analyses; systematic review of Level I RCTs and Level I studies.

Level 2: Lesser quality RCT; prospective comparative study; retrospective study; untreated controls from an RCT; lesser quality prospective study; development of diagnostic criteria on consecutive patients; sensible costs and alternatives; values obtained from limited stud- ies; with multiway sensitivity analyses; systematic review of Level II studies or Level I studies with inconsistent results.

Level 3: Case-control study (therapeutic and prognostic studies); retrospective comparative study; study of nonconsecutive patients without consistently applied reference “gold” standard; analyses based on limited alternatives and costs and poor estimates; systematic review of Level III studies.

Level 4: Case series; case-control study (diagnostic studies); poor reference standard; analyses with no sensitivity analyses.

Level 5: (lower quality of evidence) – Expert opinion.

By looking at the pyramid, you can roughly distinguish what type of research gives you the highest quality of evidence and which gives you the lowest. Basically, level 1 and level 2 are filtered information – that means an author has gathered evidence from well-designed studies, with credible results, and has produced findings and conclusions appraised by renowned experts, who consider them valid and strong enough to serve researchers and scientists. Levels 3, 4 and 5 include evidence coming from unfiltered information. Because this evidence hasn’t been appraised by experts, it might be questionable, but not necessarily false or wrong.

Examples of levels of evidence

As you move up the pyramid, you will surely find higher-quality evidence. However, you will notice there is also less research available. So, if there are no resources for you available at the top, you may have to start moving down in order to find the answers you are looking for.

• Systematic Reviews: -Exhaustive summaries of all the existent literature about a certain topic. When drafting a systematic review, authors are expected to deliver a critical assessment and evaluation of all this literature rather than a simple list. Researchers that produce systematic reviews have their own criteria to locate, assemble and evaluate a body of literature.
• Meta-Analysis: Uses quantitative methods to synthesize a combination of results from independent studies. Normally, they function as an overview of clinical trials. Read more: Systematic review vs meta-analysis .
• Critically Appraised Topic: Evaluation of several research studies.
• Critically Appraised Article: Evaluation of individual research studies.
• Randomized Controlled Trial: a clinical trial in which participants or subjects (people that agree to participate in the trial) are randomly divided into groups. Placebo (control) is given to one of the groups whereas the other is treated with medication. This kind of research is key to learning about a treatment’s effectiveness.
• Cohort studies: A longitudinal study design, in which one or more samples called cohorts (individuals sharing a defining characteristic, like a disease) are exposed to an event and monitored prospectively and evaluated in predefined time intervals. They are commonly used to correlate diseases with risk factors and health outcomes.
• Case-Control Study: Selects patients with an outcome of interest (cases) and looks for an exposure factor of interest.
• Background Information/Expert Opinion: Information you can find in encyclopedias, textbooks and handbooks. This kind of evidence just serves as a good foundation for further research – or clinical practice – for it is usually too generalized.

Of course, it is recommended to use level A and/or 1 evidence for more accurate results but that doesn’t mean that all other study designs are unhelpful or useless. It all depends on your research question. Focusing once more on the healthcare and medical field, see how different study designs fit into particular questions, that are not necessarily located at the tip of the pyramid:

• Questions concerning therapy: “Which is the most efficient treatment for my patient?” >> RCT | Cohort studies | Case-Control | Case Studies
• Questions concerning diagnosis: “Which diagnose method should I use?” >> Prospective blind comparison
• Questions concerning prognosis: “How will the patient’s disease will develop over time?” >> Cohort Studies | Case Studies
• Questions concerning etiology: “What are the causes for this disease?” >> RCT | Cohort Studies | Case Studies
• Questions concerning costs: “What is the most cost-effective but safe option for my patient?” >> Economic evaluation
• Questions concerning meaning/quality of life: “What’s the quality of life of my patient going to be like?” >> Qualitative study

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Systematic Reviews

• Levels of Evidence
• Evidence Pyramid
• Joanna Briggs Institute

The evidence pyramid is often used to illustrate the development of evidence. At the base of the pyramid is animal research and laboratory studies – this is where ideas are first developed. As you progress up the pyramid the amount of information available decreases in volume, but increases in relevance to the clinical setting.

Meta Analysis  – systematic review that uses quantitative methods to synthesize and summarize the results.

Systematic Review  – summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate st atistical techniques to combine these valid studies.

Randomized Controlled Trial – Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest.

Cohort Study – Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.

Case Control Study – study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.

Case Series   – report on a series of patients with an outcome of interest. No control group is involved.

• Levels of Evidence from The Centre for Evidence-Based Medicine
• The JBI Model of Evidence Based Healthcare
• How to Use the Evidence: Assessment and Application of Scientific Evidence From the National Health and Medical Research Council (NHMRC) of Australia. Book must be downloaded; not available to read online.

When searching for evidence to answer clinical questions, aim to identify the highest level of available evidence. Evidence hierarchies can help you strategically identify which resources to use for finding evidence, as well as which search results are most likely to be "best".                                             

Image source: Evidence-Based Practice: Study Design from Duke University Medical Center Library & Archives. This work is licensed under a Creativ e Commons Attribution-ShareAlike 4.0 International License .

The hierarchy of evidence (also known as the evidence-based pyramid) is depicted as a triangular representation of the levels of evidence with the strongest evidence at the top which progresses down through evidence with decreasing strength. At the top of the pyramid are research syntheses, such as Meta-Analyses and Systematic Reviews, the strongest forms of evidence. Below research syntheses are primary research studies progressing from experimental studies, such as Randomized Controlled Trials, to observational studies, such as Cohort Studies, Case-Control Studies, Cross-Sectional Studies, Case Series, and Case Reports. Non-Human Animal Studies and Laboratory Studies occupy the lowest level of evidence at the base of the pyramid.

• << Previous: What is a Systematic Review?
• Next: Locating Systematic Reviews >>
• Getting Started
• What is a Systematic Review?
• Locating Systematic Reviews
• Searching Systematically
• Developing Answerable Questions
• Identifying Synonyms & Related Terms
• Using Truncation and Wildcards
• Identifying Search Limits/Exclusion Criteria
• Keyword vs. Subject Searching
• Where to Search
• Search Filters
• Sensitivity vs. Precision
• Core Databases
• Other Databases
• Clinical Trial Registries
• Conference Presentations
• Databases Indexing Grey Literature
• Web Searching
• Handsearching
• Citation Indexes
• Documenting the Search Process
• Managing your Review

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• Last Updated: Sep 25, 2024 3:16 PM
• URL: https://guides.library.ucdavis.edu/systematic-reviews