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SYSTEMATIC REVIEW article

Quantifying cognitive and affective impacts of quizlet on learning outcomes: a systematic review and comprehensive meta-analysis.

• 1 Foreign Language Education, School of Foreign Languages, Selcuk University, Konya, Türkiye
• 2 Foreign Language Education, School of Foreign Languages, Akdeniz University, Antalya, Türkiye

Background: This study synthesizes research on the impact of Quizlet on learners’ vocabulary learning achievement, retention, and attitude. Quizlet’s implementation in language education is posited to enhance the learning experience by facilitating the efficient and engaging assimilation of new linguistic concepts. The study aims to determine the extent to which Quizlet influences vocabulary learning achievement, retention, and attitude.

Methods: Employing a meta-analysis approach, this study investigates the primary research question: “Does Quizlet affect students’ vocabulary learning achievement, learning retention, and attitude?” Data were collected from various databases, identifying 94 studies, of which 23 met the inclusion criteria. The coding reliability was established at 98%, indicating a high degree of agreement among experts. A combination of random and fixed effects models was used to analyze the effect size of Quizlet on each outcome variable.

Results: Quizlet was found to have a statistically significant impact on learners’ vocabulary learning achievement, retention, and attitude. Specifically, it showed moderate effects on vocabulary learning achievement ( g = 0.62) and retention ( g = 0.74), and a small effect on student attitude ( g = 0.37). The adoption of the fixed effects model for attitude was due to homogeneous distribution, while the random effects model was used for achievement and retention because of heterogeneous distribution.

Conclusion: Quizlet enhances vocabulary learning achievement, retention, and has small positive effect on learner attitude. Its integration into language education curricula is recommended to leverage these benefits. Further research is encouraged to explore the optimization of Quizlet and similar platforms for educational success.

1 Introduction

The exponential expansion of digital technologies within the realm of pedagogy has sparked an escalating curiosity in scrutinizing their effects on academic achievement among students. This surge in interest calls for a thorough examination of how these technological tools are reshaping educational practices and outcomes. Students are frequently referred to as “Digital Natives” on account of their innate fluency with various technological devices such as computers, the internet, and video games ( Prensky, 2009 ). This inherent proficiency has been pivotal in driving the integration of digital tools in educational settings. The seamless incorporation of these technologies into classrooms, particularly language learning classrooms, highlights the evolving dynamics of modern education and emphasizes the need for empirical research to assess their impact. The field of language education has undergone a significant transformation due to the increasing influence of technology, resulting in a shift towards the integration of computers, mobile devices, and technology into teaching and learning practices ( Aprilani, 2021 ). This paradigm shift demonstrates the critical role of technology in facilitating innovative teaching and learning strategies and thus improving the quality and accessibility of education. This integration has not only reshaped traditional educational methodologies but has also necessitated the incorporation of information technology (IT) into the teaching and learning process ( Eady and Lockyer, 2013 ). As a result, the academic community is increasingly focused on understanding the impact of these changes on pedagogical practices, teaching and learning processes and student outcomes. In the domain of language education, the utilization of mobile technology has the capacity to transcend the constraints imposed by conventional learning methodologies in terms of spatial and temporal limitations, which ultimately caters to the individualized learning requirements of contemporary tertiary level scholars ( Lin and Chen, 2022 ). This situation emphasizes the importance of investigating the effectiveness of mobile technologies in improving the quality of the learning process in language education and meeting the different needs of learners. Moreover, the global application of technology in English teaching and learning has been instrumental, benefiting both teachers and learners by facilitating classroom activities and accelerating language acquisition through the use of technology and its services ( Nguyen and Van Le, 2022 ). Moreover, the integration of technology within the language learning milieu cultivates a heightened sense of self-directed and malleable learning methodology. Studies conducted on the domain of Computer-Assisted Language Learning (CALL) and Mobile-Assisted Language Learning (MALL) have inferred that the application of technological tools in the language learning process especially in the acquisition of vocabulary, particularly for non-native speakers, can be an efficacious strategy ( McLean et al., 2013 ; Chatterjee, 2022 ). This body of research provides a compelling rationale for investigating specific digital tools like Quizlet and their potential to enhance language learning. As this digital transformation in language education continues, it becomes critical to examine specific digital tools and their unique contributions to this evolving educational paradigm, especially how they combine traditional methods with innovative technology-based strategies. Amidst this technological revolution in education, the role of specific tools such as Quizlet becomes increasingly significant. By focusing on Quizlet, this study aims to bridge the gap in the literature regarding the effectiveness of digital tools in enhancing vocabulary acquisition among language learners. Integrating technology into the language learning environment fosters a sense of independent and flexible learning methodology, especially in terms of vocabulary acquisition for non-native speakers. It is precisely at this point that the functionality and applicability of tools such as Quizlet, as part of the trend in digital education, becomes important in representing an intersection between traditional learning methodologies and modern, technology-enhanced approaches. Therefore, this study seeks to contribute to the broader discourse on digital education by examining the impact of Quizlet on vocabulary learning, retention and attitude, thereby offering insights into its role as a transformative tool in language education. By systematically reviewing and meta-analyzing existing literature, our study aims to provide a definitive assessment of Quizlet’s role in the digital education landscape, highlighting its potential as a transformative educational tool.

2 Literature review

In light of this reality, a myriad of applications with a focus on improving cognitive and emotional aspects of learners have surfaced on the internet, a substantial proportion of which can be readily downloaded and employed by users without incurring any costs. This proliferation of digital resources presents a convenient and easily accessible means for language learners to supplement their vocabulary acquisition, retention, motivation and attitude endeavors. An exemplar of such innovative technological solutions is Quizlet, a widely utilized online platform that provides a diverse array of educational tools, comprising interactive flashcards, gamified activities, and evaluation assessments, among others.

Andrew Sutherland designed a learning aid in 2005 that facilitated his academic excellence in French vocabulary assessment. He imparted it to his peers, and it resulted in a similar achievement in their respective assessments. Quizlet has since emerged as a powerful educational resource that has gained immense popularity, serving more than 60 million students and learners each month. Its widespread usage spans a wide range of disciplines, including mathematics, medicine, and foreign language acquisition, among others ( Quizlet, 2023 ). Quizlet provides a platform that enables learners to curate personalized study materials consisting of conceptual units coupled with their corresponding definitions or elucidations. Learners engage with these instructional modules through varied modes of learning, such as flashcards, games, and quizzes ( Fursenko et al., 2021 ). It is a popular web-based platform that offers a range of study tools, including flashcards, games, and quizzes. Quizlet is a well-known online learning application that enables users to build and study interactive resources like games and flashcards. According to Quizlet (2023) , learning can be improved by using it in a variety of contexts and areas. The Quizlet mobile application is particularly effective for constructing vocabulary content. It has been proposed as a convenient and pleasurable method for acquiring vocabulary knowledge ( Davie and Hilber, 2015 ). Within the app, users can access vocabulary “sets” created by other users, or they can generate their own sets and access them as flashcards or through a gaming interface ( Senior, 2022 ). Quizlet is renowned for its distinctive attributes that pertain to the creation of flashcards, multilingual capacity, and the ability to incorporate images, among other forms of diverse exercises. However, it lacks the provision of scheduling and expanded retrieval intervals as the learning process advances. There are various ways in which vocabulary sets in Quizlet can be disseminated, including but not limited to printing, embedding, incorporating URL links, and utilizing QR codes. These options provide a range of alternatives for learners to study at their preferred pace, allowing for individualized and autonomous learning experiences ( Waluyo and Bucol, 2021 ). This shift places Quizlet within a broader movement towards digitalization in education, juxtaposing its role with other emerging educational technologies.

The implementation of Quizlet in language education can potentially augment the learning experience and facilitate the assimilation of new linguistic concepts in a more efficient and engaging manner ( Wang et al., 2021 ). While many educators and students have claimed that Quizlet improves cognitive and emotional learning outcomes, the empirical evidence supporting this claim has been mixed. Alastuey and Nemeth (2020) discussed the effects of Quizlet on vocabulary acquisition, highlighting the cognitive, affective, and motivational benefits for students creating their own learning material. However, Nguyen and Van Le (2022) pointed out the limited empirical research on the effectiveness of Quizlet, indicating a gap in the evidence. İnci (2020) reported that the use of the application in foreign language lessons improved learner engagement of learners. On the other hand, Berliani and Katemba (2021) found that most students considered Quizlet effective in learning vocabulary, supporting the positive impact on cognitive and emotional learning outcomes. Additionally, Setiawan and Wiedarti (2020) reported that the Quizlet application positively influences students’ performance and motivation in learning vocabulary. Therefore, while some studies support the claim of Quizlet’s positive effects on cognitive and emotional learning outcomes, there is also a need for further empirical research to provide a more comprehensive understanding of its impact. Nguyen et al. (2022) found that Quizlet positively influences students’ performance and autonomy in learning vocabulary ( Nguyen et al., 2022 ). Similarly, Sanosi (2018) conducted an experimental-design study that investigated the effect of Quizlet on vocabulary acquisition, highlighting its potential for enhancing vocabulary learning ( Anjaniputra and Salsabila, 2018 ; Sanosi, 2018 ) reported that Quizlet fostered learners’ engagement and persistence in vocabulary learning, indicating its usefulness as a learning tool ( Anjaniputra and Salsabila, 2018 ). Furthermore, Alastuey and Nemeth (2020) examined the use of Quizlet in an urban high school language arts class and demonstrated that students using Quizlet outperformed those in the Non-Quizlet group on weekly vocabulary tests, emphasizing its positive impact on vocabulary acquisition ( Alastuey and Nemeth, 2020 ; Setiawan and Wiedarti, 2020 ) found that the Quizlet application positively influenced students’ performance and autonomy in learning vocabulary, further supporting its effectiveness ( Setiawan and Wiedarti, 2020 ). These findings align with the research by Körlü and Mede (2018) , which indicated that Quizlet had a positive impact on students’ performance and autonomy in vocabulary learning ( Körlü and Mede, 2018 ). Also, several studies have demonstrated the positive influence of Quizlet on student’s cognitive learning such as vocabulary learning and retention ( Barr, 2016 ; Özer and Koçoğlu, 2017 ; Ashcroft et al., 2018 ; Körlü and Mede, 2018 ; Sanosi, 2018 ; Andarab, 2019 ; Çinar and Ari, 2019 ; Toy, 2019 ; Arslan, 2020 ; Chaikovska and Zbaravska, 2020 ; Tanjung, 2020 ; Van et al., 2020 ; Akhshik, 2021 ; Aksel, 2021 ; Fursenko et al., 2021 ; Ho and Kawaguchi, 2021 ; Kurtoğlu, 2021 ; Setiawan and Putro, 2021 ; Atalan, 2022 ; Lin and Chen, 2022 ; Nguyen and Van Le, 2022 , 2023 ).

However, these studies also show that the effectiveness of tools such as Quizlet can vary considerably depending on various factors such as students’ readiness, the teaching-learning process, the learning environment and the type of language skill targeted. Along these lines, a critical review of how Quizlet affects learning outcomes is still evolving. While some studies demonstrate the positive effects of technologies such as Quizlet, others offer a more cautious view, painting the other side of the coin and pointing to limitations and variable outcomes in different educational contexts. For example, some students prefer Quizlet because of its convenience, usefulness, practicality and effectiveness, while others express dissatisfaction with certain features and errors ( Pham, 2022 ). Moreover, the effectiveness of Quizlet in vocabulary learning has been a subject of research, with some studies indicating its success in enhancing vocabulary acquisition and retention ( Körlü and Mede, 2018 ; Al-Malki, 2020 ; Mykytka, 2023 ), while others suggest that its use does not necessarily lead to autonomous learning ( Setiawan and Wiedarti, 2020 ).

Given the varied and sometimes contradictory findings of related studies in the literature, a more general, systematic and comprehensive approach is needed to understand the real impact of Quizlet on learning outcomes. While generally positive in the literature, the different perspectives and diverse results reported highlight the complexity of evaluating the effectiveness of digital learning tools such as Quizlet. This underlines the need for a more comprehensive, nuanced and evidence-based evaluation and is the main focus of the current research. Unfortunately, there is little and contradictory empirical data to support Quizlet’s impact on learning outcomes. As a result, the purpose of this research is to consolidate and assess the body of knowledge on the effect of Quizlet on learning outcomes through a thorough meta-analysis and systematic review. This research aims to fill the existing gap in empirical research, provide valuable insights, and contribute to the literature in terms of having a final say on the broader understanding of Quizlet’s effectiveness in language learning. Consequently, a comprehensive and systematic review of the existing literature is warranted to evaluate the impact of Quizlet especially on student emotional learning outcomes. This meta-analysis aims to fill this gap by synthesizing the available research on Quizlet and providing a quantitative assessment of its effectiveness in enhancing student cognitive and emotional learning outcomes. By conducting a systematic review and comprehensive meta-analysis, this research aims to determine whether Quizlet’s utilization leads to a significant difference in student outcomes in these key areas compared to traditional or alternative learning methods. Through a rigorous and transparent synthesis of the empirical evidence, this study seeks to shed light on the potential of Quizlet to improve student cognitive and emotional learning outcomes and inform future research and practice in the field of digital education.

The detailed literature review revealed a scarcity of quantitative studies suitable for a meta-analysis, particularly concerning the effects of Quizlet on aspects such as student motivation, confidence, learner engagement, and anxiety. Consequently, this study focuses on quantifying the impact of Quizlet on foreign language learners’ vocabulary learning achievement, retention, and attitude through a systematic review and comprehensive meta-analysis. The study investigates whether the use of Quizlet results in a significant difference in student scores in these areas compared to other learning methods.

3 Methodology

3.1 model of the research.

In this study, we conducted a comprehensive examination of quantitative research focusing on the application of Quizlet in vocabulary learning. The selection of studies for this meta-analysis was guided by systematic and rigorous methods, as recommended by the PRISMA guidelines. In accordance with PRISMA guidelines, researchers have employed systematic review and meta-analysis methodologies to ensure transparency, reproducibility, and rigor in their studies ( Page et al., 2021 ). The PRISMA guidelines provide a comprehensive checklist for reporting systematic reviews and meta-analyses, encompassing various aspects such as study selection, data extraction, and synthesis methods ( Page et al., 2021 ). Adhering to these guidelines enhances the quality and reliability of the research findings, thereby contributing to evidence-based decision-making in diverse fields.

This study involved a comprehensive search of literature from the inception of Quizlet in 2005 to the present year, 2023. Our focus on the period from 2016 to 2023 is based on the emergence of a pivotal study in 2016, which was the first to explore the impact of Quizlet on the identified outcomes. Our analysis encompassed a broad spectrum of educational settings and demographics, reflecting the diverse populations engaged in using this tool. The core intervention we scrutinized was Quizlet’s utilization for enhancing vocabulary learning, its retention, and its influence on learner attitudes. To gauge Quizlet’s efficacy, we included studies that provided a comparative analysis between Quizlet and traditional learning methodologies or other educational technologies. This comparative approach enabled us to assess the relative effectiveness of Quizlet in achieving the desired educational outcomes. Our primary outcomes of interest were learners’ achievement in vocabulary acquisition, the retention of this knowledge over time, and their attitudes towards the use of Quizlet as a learning tool. The temporal scope of our review was strategically chosen, with 2016 marking the emergence of a pivotal study that set a precedent in this research area, thereby shaping the subsequent investigations into Quizlet’s impact in educational contexts. In accordance with PRISMA guidelines, we have employed a meta-analytic survey approach to determine the effect size of Quizlet’s impact on foreign language learners’ vocabulary learning, retention, and attitudes. This includes a thorough evaluation of study quality, risk of bias, and the applicability of findings.

3.2 Data collection and coding

In the course of gathering data for this research, an examination of diverse databases was conducted, encompassing the YÖK national thesis center, Google Scholar, Selcuk University Academic Search Engine, DergiPark, Proquest, Sage Journals, Eric, Wiley Online Library, Taylor & Francis Online, Science Direct, Jstor, and Springer Link databases. Throughout this phase, the fundamental concepts under consideration were “Quizlet” and “mobile flashcards.” In the preliminary scrutiny of this research, a comprehensive total of 94 studies were discerned. Nevertheless, 71 of these studies were omitted from the meta-analysis owing to their qualitative nature, irrelevant outcomes such as absence of exploration into academic achievement, learning retention, student attitude, and the format such as the transformation from thesis to article format. A significant number of studies were based on qualitative research methodologies. While these studies provide valuable insights, our meta-analysis focused on quantifiable outcomes that could be statistically analyzed. Therefore, studies that primarily employed qualitative methods such as interviews, narrative analysis, or case studies were excluded. Several studies did not align with the specific outcomes of interest for our research. Our meta-analysis aimed to explore the impact of “Quizlet” on academic achievement, learning retention, and student attitudes. Studies that did not investigate these specific outcomes, or that focused on peripheral aspects not directly related to our research questions, were omitted. This included studies that might have used similar tools or technologies but did not measure the outcomes relevant to our analysis. For studies that were available in both thesis and article formats, we chose to exclude the thesis versions. This decision was made because our research aimed to understand how the condensation and refinement involved in transforming a thesis into a journal article could impact the presentation and interpretation of research findings. Including both formats of the same study could lead to redundancy and skew the meta-analysis results. Flow chart in ( Figure 1 ) shows the process of scanning the literature and inclusion–exclusion of accessed studies in meta-analysis.

Figure 1 . Flow chart showing the process of scanning the literature and inclusion of accessed studies in meta-analysis.

To ensure systematic data analysis, we employed a two-stage coding process. In the first stage, each study was preliminarily coded based on its relevance to our key concepts. This step helped in filtering out studies that did not directly contribute to our research questions. The second stage involved a more detailed coding procedure, where two independent researchers coded the remaining studies for more specific variables such as research methodology, population, outcomes measured, and main findings. Any discrepancies between the coders were resolved through discussion and consensus, ensuring a high degree of inter-coder reliability. This step was crucial in maintaining the objectivity and consistency of the data coding process. The validity and reliability calculations related to the coding process are discussed in detail in the section titled “Reliability and validity of the research” of this study.

3.3 Inclusion criteria

Prescribed protocols are advised for the execution of meta-analyses, as delineated by Field and Gillett (2010) and Bernard et al. (2014) . Fundamentally, these scholars advocate for a meticulous assessment of the literature search process and a thorough evaluation of the selected studies with regard to potential publication bias, which should be undertaken prior to the initiation of pertinent statistical analyses. In order to be incorporated into the meta-analysis, prospective studies were required to conform to several specific eligibility criteria. Firstly, an eligible study had to investigate the impact of Quizlet. Secondly, the study had to make a comparative assessment of the impact of Quizlet in relation to a control group. Prospective-pre-post designs that did not incorporate a control or comparison group were excluded from consideration, as they failed to account for potential influences stemming from natural development or extraneous variables. Additionally, in order to meet the inclusion criteria, a study had to be conducted within an educational setting or possess a clear relevance to educational outcomes. This encompassed all levels of education, spanning from tertiary to secondary and primary levels. Furthermore, an eligible study was required to furnish adequate data for the computation of an effect size. Figure 1 reflects flow chart of the process of scanning the literature and inclusion of accessed studies in meta-analysis.

In order to ensure comprehensive coverage, a meticulous internet search was carried out according to the inclusion criteria mentioned in Figure 1 and a total of 94 studies were initially identified related to the topic. During the screening process, a significant portion of these studies were excluded due to several factors. Excluded studies included non-parametric data, qualitative features, quantitative data, and studies that did not examine the effects of Quizlet on cognitive and emotional outcomes. Exclusion of studies with qualitative characteristics was necessary since they did not comply with the quantitative methodology needed for this meta-analysis. Some studies were excluded due to the lack of control groups. The inclusion of both control and experimental groups in studies is crucial for ensuring the validity of research findings. The importance of experimental and quasi-experimental designs for generalized causal inference in meta-analyses of research is emphasized in literature ( Preece, 1983 ; Anderson-Cook, 2005 ; Morris, 2007 ). By meticulously applying these inclusion criteria, the meta-analysis carefully selected studies with precision. This thorough approach ensured that only the most relevant and suitable sources were included, thereby enhancing the overall quality and reliability of the analysis. To measure the effects of the Quizlet on vocabulary learning achievement, retention, and attitude, 23 carefully selected studies that met the inclusion requirements made up the study’s sample. These studies had a range of sample sizes and covered a range of study types. Table 1 provides a detailed summary of the publication year, study type, research courses, and sample sizes of the included studies, giving a clear picture of the make-up of the meta-analysis sample.

Table 1 . Features of the studies included in the meta-analysis.

3.4 Reliability and validity of the research

When performing meta-analysis studies, it is imperative to methodically assemble descriptive data that highlights the important aspects of the included research. Careful data collection is necessary for this, where relevant information is meticulously recorded to facilitate additional analysis. The process of coding in meta-analysis studies is crucial for converting descriptive data into numerical data, enabling statistical analysis ( Neyeloff et al., 2012 ). Coding processes are essential for the synthesis of data and are used to convert descriptive data into a format that can be subjected to statistical analysis ( Berkeljon and Baldwin, 2009 ). According to Karadağ et al. (2015) , coding is a methodical and scientific approach that is utilized to extract pertinent and accurate data from the massive amount of data that is collected throughout the investigations.

In the coding process of this study to guarantee the accuracy of the coding process, a stringent methodology was developed. The coding was done in compliance with the coding form, which was established prior to the analysis. Creating a unique coding system that was both general and distinct enough to capture the features of any kind of research was the primary goal of this process. The coding process was done independently by two experts, each with extensive knowledge and expertise in the field. The coding forms completed by the first and second experts were carefully compared in order to assess the level of agreement between them. The calculation of Inter-rater Reliability (IRR) can be quantitatively assessed using the formula agreement/(agreement + disagreement) x 100. This formula enables a quantitative assessment of the consistency between the two experts’ coding ( Hripcsak and Rothschild, 2005 ). It is important to note that the calculation of IRR is crucial in various fields, including medical informatics, forensic psychology, and educational measurement ( Hripcsak and Heitjan, 2002 ; Cook et al., 2008 ; Guarnera and Murrie, 2017 ). The use of this formula allows for the measurement of specific agreement, which is essential in quantifying interrater reliability and assessing the reliability of a gold standard in various studies ( Hripcsak and Heitjan, 2002 ). The calculated Inter-rater Reliability (IRR) score provided a measure of the degree of agreement between the two experts, indicating the reliability of the coding process. In this study, the reliability was determined to be 98%, signifying a high level of concordance between the experts’ assessments. The high reliability score of this meta-analysis enhances the overall reliability and robustness of the results by providing assurance about the coding process’s precision and consistency.

3.5 Data analysis procedure

This study utilizes Hedges’s g as the measurement unit for effect size. A significance level of 95% is established. The total effect size is then determined by first calculating the effect sizes for each study included in the meta-analysis. Two models, namely fixed effects and random effects are employed to determine the overall effect size.

The effect sizes obtained from the analyses were interpreted using the effect size classification proposed by Thalheimer and Cook (2002) and Hunter and Schmidt (2015) . These researchers discuss methods of meta-analysis and provide insights into the interpretation of effect sizes. According to them, the classification of effect sizes as small (0.15 ≤ Hedges’s g  < 0.40), moderate (0.40 ≤ Hedges’s g  < 0.75), large (0.75 ≤ Hedges’s g  < 1.10), very large (1.10 ≤ Hedges’s g  < 1.45), and excellent (Hedges’s g  ≥ 1.45). These references provide a comprehensive understanding of the interpretation of effect sizes, aligning with the specified ranges for Hedges’s g .

This study’s data analysis produced several noteworthy conclusions, which are discussed in more detail below.

4.1 Effect size

The effect size, represented as “d,” was determined as the result of dividing the discrepancy between the treatment conditions by the amalgamated standard deviation of the two study groups ( Borenstein et al., 2021 ). Cohen’s d or Hedges’ g represent the effect size when utilizing contrast groups ( Hedges, 1983 ; Hedges and Olkin, 1985 ; Cohen, 1988 ; Hartung et al., 2008 ; Borenstein et al., 2009 ). Hedges’ g is particularly useful for small sample sizes and is preferred when the studies being compared have different sample sizes or variances ( Light et al., 1994 ).

The decision on whether to use a fixed effects model or a random effects model for calculating effect sizes in a study is crucial. Calculating effect sizes “d” and “g” by dividing the discrepancy between the means of each group’s experimental and control cohorts by their pooled standard deviations is a purposeful and meaningful procedure ( Borenstein et al., 2009 ). While the random effects model aims to generalize findings beyond the included studies by assuming that the selected studies are random samples from a larger population, the fixed effects model is ideal for drawing conclusions on the studies included in the meta-analysis ( Cheung et al., 2012 ). The random effects model is a good option for meta-analysis when the goal is to make the results more broadly applicable than the individual research. A random effects model takes into account both within- and between-study variation, making it more cautious and producing a broader confidence interval ( Ma et al., 2015 ). The second criterion is dependent upon the number of studies that are included in the meta-analysis. The fixed effects model is considered appropriate when the number of studies is less than five ( Aydin et al., 2020 ). Studies are deemed homogenous if the variance in effect sizes amongst them is only attributable to sampling error; in a meta-analysis, this source of variation can be accounted for by employing the fixed effect model ( Idris and Saidin, 2010 ). The random effects model assumes a normal distribution of genuine effect sizes and estimates the mean and variance of this distribution, whereas the fixed effects model assumes a common true effect size across all studies and calculates this common effect size ( Spineli and Pandis, 2020 ). The third criterion is whether statistical heterogeneity exists between effect sizes. The random effects model must be used when heterogeneity is found, as explained by Tufanaru et al. (2015) . A random effects model, which takes into account both within- and between-study variance, can be more suited if there is significant heterogeneity among the studies. Conversely, a fixed effects approach would be more appropriate if the trials are quite homogeneous ( Danos, 2020 ). It is important to consider the assumptions and implications of each model when making this decision, as the choice of model can impact the interpretation and generalization of the results ( Konstantopoulos, 2006 ).

In this study, the statistical data on vocabulary learning and retention of Quizlet application were interpreted according to the random effects model since they showed heterogeneous distribution (see Tables 2 , 3 ), and the data on student attitude were interpreted according to the fixed effects model since they showed homogeneous distribution (see Table 4 ).

Table 2 . Homogeneity test results: Q -statistic, I 2 and tau-square statistics assessing the impact of Quizlet on vocabulary learning achievement.

Table 3 . Homogeneity test results: Q -statistic, I 2 and tau-square statistics assessing the impact of Quizlet on vocabulary retention.

Table 4 . Homogeneity test results: Q-statistic, I 2 and tau-square statistics assessing the impact of Quizlet on student attitude.

4.2 The meta-analysis outcomes pertaining to the influence of Quizlet on vocabulary learning achievement

In pursuit of addressing the primary research query, the study sought to ascertain the extent to which Quizlet, as supported by experimental study findings, contributes to students’ vocabulary learning. To unravel this quandary, meticulous analyses were conducted on the pertinent data extracted from the studies encompassed within the research. Heterogeneity in the context of meta-analysis refers to sampling error and the variation in results seen across many research papers ( Borenstein et al., 2009 ). To evaluate the degree to which the conclusions of each research study are influenced by both the sampling error and the fluctuation or population variance in the estimated effect size, it becomes essential to conduct a heterogeneity assessment. The results of the heterogeneity test also help to identify if the study fits better with a fixed effect model or a random effect model. As a result, any of these impact models is used to calculate the effect magnitude or summarizing effect of the study’s findings for further research. In this work, heterogeneity testing is examined using Q-statistics in conjunction with its p -value, I 2 and τ 2 parameters, all of which are listed in Table 2 .

According to the homogeneity test in Table 2 , the average effect size Q-statistical value of the Quizlet on vocabulary learning is calculated as 113.069 at 20 degrees of freedom at 95% significance level and is found to be statistically significant ( Q  = 113.069; p  < 0.05). According to the Q -value results of the research data, it can be said that the distribution is heterogenous. The tau-square value (τ 2 ), which estimates the variance of the true mean effect size, is calculated as (τ 2 ) 0.284, and the I 2 statistic is calculated as 82.312. This I 2 value calculated for the vocabulary learning variable indicates that we can explain 82.312% of the variance in the average effect size calculated in the studies included in the meta-analysis with the data we have and indicates a high level of heterogeneity.

In Figure 2 , the lines flanking the squares represent the lower and upper bounds of effect sizes within a 95% confidence interval, while the rhombus indicates the overall effect size of the studies. Upon examination, the smallest effect size is −0.408, and the largest is 2.083. The weight percentage provided alongside the effect size values quantitatively represents the contribution of each study to the overall outcome of the meta-analysis.

Figure 2 . Effect size values related to vocabulary learning achievement.

The results that are provided in Table 5 indicate that Quizlet has moderate impact on vocabulary learning. These empirical results highlight the critical need and effectiveness of using Quizlet as an instructional tool to help students develop higher order lexical knowledge. Using the Classic Fail-Safe N analysis, a technique used to determine the strength of the meta-analysis under consideration, it was confirmed that Quizlet has a modest effect (effect size, g  = 0.62) on the improvement of vocabulary proficiency. Table 6 presents the Classic Fail-Safe N Analysis of this examination, providing additional insight into the validity and strength of the determined outcomes. Classic fail-safe N analysis is utilized to determine the stability of results and to identify the potential impact of unpublished studies on the overall conclusions of a meta-analysis ( Erford et al., 2010 ) and it provides an indication of the robustness of the findings and is employed to evaluate the stability of the meta-analytic results ( Acar et al., 2017 ).

Table 5 . Average effect sizes and confidence interval lower and upper values by effect model.

Table 6 . Classic fail-safe N analysis.

Based on the Classic Fail-Safe N analysis, it becomes apparent that an additional 590 studies would be necessary to potentially alter the conclusion drawn from the meta-analysis, suggesting that Quizlet’s impact on vocabulary learning is either negligible or negative ( p  < 0.05). The inclusion of these 590 studies reporting no substantial impact of Quizlet on vocabulary learning would be pivotal to reconsidering the overall outcome of the meta-analysis. Their incorporation would significantly enhance the breadth of evaluation regarding Quizlet’s relationship with vocabulary learning, enriching our understanding of its potential effects as an instructional tool.

Figure 3 illustrates the distribution of effect sizes in accordance with Hedges’s funnel chart (Funnel plot of precision). The funnel plot is a widely used tool in meta-analysis to visually assess the presence of publication bias and small-study effects ( Egger et al., 1997 ). It provides a graphical display of the relationship between the effect size estimates and a measure of study precision, such as the standard error or sample size ( Kiran et al., 2016 ). Funnel plots are particularly useful in exploring sources of heterogeneity and bias in meta-analyses ( Schild and Voracek, 2013 ). These graphical representations not only aid in visualizing the effect size distribution but also underscore the importance of assessing publication bias in meta-analytical studies, ensuring a comprehensive and unbiased evaluation of Quizlet’s impact on vocabulary learning achievement.

Figure 3 . Funnel plot on publication bias of studies examining the effect of Quizlet on vocabulary learning achievement.

According to Figure 3 , it becomes evident that the investigations fail to exhibit an asymmetrical distribution with respect to the overall effect size. The funnel’s edge in the graphic is marked by a ± slope. Figure 3 reveals that significant differences or anomalies in distribution are conspicuously missing. To put it differently, the distribution does not display a pronounced concentration on one side. The graphic clearly conveys that there are many studies that are located outside of the funnel, highlighting the significant diversity that exists within this cohort and making it possible to say that the group is heterogeneous. Our thorough investigation turned up no concrete proof of publication bias among the variety of research we included in our meta-analysis. The absence of an asymmetric clustering at a singular point within the distribution signifies that the study sample does not exhibit a predisposition towards favoring the Quizlet, thereby enhancing the reliability of this meta-analysis study.

Table 7 meticulously catalogues the results of the Begg and Mazumdar rank correlation test. This statistical test evaluates the relationship between the standardized treatment effect and the variance of the treatment effect using Kendall’s tau ( Gjerdevik and Heuch, 2014 ).

Table 7 . Begg and Mazumdar rank correlation.

In Table 7 , the Begg and Mazumdar rank correlation test has unveiled that the composite study sample integrated into the meta-analysis does not demonstrate any signs of bias (tau b  = 0.25; p  > 0.05). Consequently, the findings derived from the scrutiny of effect sizes originating from the constituent studies are deemed to possess a high degree of reliability. This signifies that the inferences drawn from the meta-analysis concerning the influence of the Quizlet on the assessed parameters can be characterized as sturdy and trustworthy. These results highlight the validity and reliability of the conclusions drawn from our research, which can be regarded as robust and unwavering.

4.3 The meta-analysis outcomes pertaining to the influence of Quizlet on vocabulary retention

The secondary inquiry in this study aimed to ascertain the impact of Quizlet on retaining vocabulary. To address this, a meticulous analysis of relevant data gleaned from the research was undertaken. Homogeneity assessments, as detailed in Table 3 , were conducted to ascertain the suitability of employing either the fixed effects model or the random effects model for computing the effect sizes associated with the influence of Quizlet on vocabulary retention. These assessments aimed to discern the best approach to quantify the impact of Quizlet on the retention of vocabulary across different study conditions or populations. Moving from these methodological decisions, the subsequent focus lay in interpreting the implications of Quizlet’s influence on vocabulary retention within diverse study contexts.

As a result of the homogeneity test, the average effect size Q -statistical value of the Quizlet on vocabulary retention is calculated as 20.997 at 4 degrees of freedom at 95% significance level and is found to be statistically significant ( Q  = 20.997; p  < 0.05). According to the Q-value results of the research data, it can be said that the distribution is heterogenous. The tau-square value (τ 2 ), which estimates the variance of the true mean effect size, is calculated as (τ 2 ) 0.259, and the I 2 statistic is calculated as 80.947. This I 2 value calculated for the vocabulary retention variable indicates that we can explain 80.947% of the variance in the average effect size calculated in the studies included in the meta-analysis with the data we have and indicates a high level of heterogeneity.

In Figure 4 , the lines bordering the squares depict the range of effect sizes encompassed by a 95% confidence interval, with the rhombus denoting the aggregate effect size derived from the studies. Analysis reveals effect sizes ranging from 0.000 to 1.217. Additionally, the weight percentage accompanying each effect size quantifies the relative impact of individual studies on the collective result of the meta-analysis. This visual representation not only delineates the variability in effect sizes but also emphasizes the influence of each study on the overall outcome, providing a nuanced understanding of the meta-analytical findings.

Figure 4 . Effect size values related to vocabulary retention.

The findings outlined in Table 8 demonstrate that Quizlet exerts a moderate impact on vocabulary retention (Hedges’ g  = 0.743). Employing the Classic Fail-Safe N analysis, a method aimed at gauging the robustness of the meta-analysis, affirmed the moderate effect of Quizlet ( g  = 0.74) in advancing vocabulary retention. Table 9 within the study further expounds upon this analysis, offering deeper insights into the credibility and potency of the conclusions drawn from the investigation. This robust analysis not only validates the efficacy of Quizlet but also emphasizes its substantive contribution to enhancing vocabulary retention among learners.

Table 8 . Average effect sizes and confidence interval lower and upper values by effect model.

Table 9 . Classic fail-safe N analysis.

Classic Fail-Safe N analysis reveals that an additional 44 studies would be required to potentially modify the conclusion drawn from the meta-analysis. This indicates a possibility that Quizlet’s impact on vocabulary retention might be insignificant or even negative ( p  < 0.05). The inclusion of these 44 studies, which report no substantial impact of Quizlet on vocabulary retention, would be crucial in reconsidering the overall outcome of the meta-analysis. Their inclusion would significantly broaden the scope of the evaluation concerning Quizlet’s association with vocabulary retention, thereby enriching our understanding of its potential as an instructional tool. Additionally, Figure 5 demonstrates the distribution of effect sizes based on Hedges’s funnel chart (Funnel plot of precision).

Figure 5 . Funnel plot on publication bias of studies examining the effects of Quizlet on vocabulary retention.

Figure 5 displays a funnel plot illustrating the distribution of effect sizes across studies. The funnel in the plot is bounded by a ± slope. The graphic indicates that some studies fall outside the slope curve, suggesting heterogeneity within the group.

Based on the data synthesized in Table 10 , employing the Begg and Mazumdar rank correlation test revealed no indications of bias within the combined study sample used in the meta-analysis (tau b  = 0.60; p  > 0.05). As a result, the scrutiny of effect sizes extracted from these studies is considered highly reliable. This substantiates the robustness of the conclusions drawn from the meta-analysis, specifically regarding Quizlet’s influence on the evaluated parameters. These outcomes not only affirm the validity and reliability of our research findings but also underscore the steadfastness and solidity of the conclusions derived. It emphasizes the credibility of our study’s outcomes, reinforcing the confidence in the observed effects of Quizlet on the assessed parameters.

Table 10 . Begg and Mazumdar rank correlation.

4.4 The meta-analysis outcomes pertaining to the influence of Quizlet on student attitude

As a result of the homogeneity test, the average effect size Q -statistical value of the Quizlet on student attitude is calculated as 2.003 at 1 degree of freedom at 95% significance level and is found to be statistically insignificant ( Q  = 2.003; p  > 0.05). According to the Q -value results of the research data, it can be said that the distribution is homogenous. The tau-square value (τ 2 ), which estimates the variance of the true mean effect size, was calculated as (τ 2 ) 0.065, and the I 2 statistic is calculated as 50.081. This I 2 value calculated for the student attitude variable indicates that we can explain 50.081% of the variance in the average effect size calculated in the studies included in the meta-analysis with the data we have and indicates a high level of homogeneity. Since the results of the homogeneity test analysis and I 2 statistics indicate that the studies on the average effect size of the Quizlet on student attitude does not differ statistically from each other, the analyses were calculated according to the fixed effects model ( Figure 6 ).

Figure 6 . Effect size values related to student attitude.

It is seen that the weights of the studies in the meta-analysis are close to each other. It can be visually understood from the forest plot that the effect sizes are generally concentrated at a low level and the overall effect size is low in width.

The meta-analysis values of the results obtained from the 2 studies included in the meta-analysis are given in Table 11 . Table 11 shows the homogeneous distribution value, average effect size and confidence intervals of the studies according to the effect model.

Table 11 . Average effect sizes and confidence interval lower and upper values by effect model.

The findings outlined in Table 11 demonstrate that Quizlet exerts a small impact on student attitude (Hedges’ g  = 0.377). According to the fixed effects model, the lower limit of the 95% confidence interval is 0.029, the upper limit is 0.725. Classical Fail-Safe N analysis, Funnel Plot and Begg and Mazumdar Rank Correlation values could not be calculated since the number of studies examining the effect of Quizlet on student attitude according to the inclusion criteria of this study was limited to 2 in the literature.

5 Discussion

The objective of this meta-analysis was to analyze the overall results acquired from studies that examined the impact of Quizlet on foreign language learners’ cognitive and emotional outcomes such as vocabulary learning achievement, retention, and attitude. This study synthesized previous research to determine the Quizlet’s impact level. The trustworthiness of the research findings is demonstrated by the confidence intervals derived from the meta-small analysis. A thorough examination of the Quizlet’s effect on numerous outcome measures was made possible by the combination of experimental and quasi-experimental research.

To begin with, the study’s first research issue focuses on the impact of Quizlet on students’ vocabulary learning achievement as measured by experimental experiments. To address this topic, a meta-analysis incorporating 21 relevant studies was conducted. To determine whether the fixed effects model or the random effects model is appropriate for the research, a homogeneity test was first carried out. The homogeneity test results showed a statistically significant difference ( Q = 113.069; p < 0.05), indicating a diverse distribution of effect sizes among the studies. A further indication of the significant degree of variability among the studies was the obtained I 2 value of 82.312%. The random effects model was used to calculate effect estimates because of the significant heterogeneity that was seen. According to the random effects model, the average effect size of the studies included in the meta-analysis on vocabulary learning achievement was calculated as 0.62 ( g = 0.62). The findings of the meta-analysis showed an increase in vocabulary learning achievement in favor of students who were involved in the learning and teaching process using Quizlet. In terms of vocabulary learning achievement, it was found that the size of effect falls in the moderate interval. This modest effect size emphasizes the nuanced role of digital tools in education, where the impact of technology is significant but not uniformly variable across settings and groups of learners. The adoption of technologically enhanced learning environments, such as the use of Quizlet, signals a broader shift towards digital literacy and its integration into educational frameworks. Also, this effect can be explained by the rapid adaptation of students to technological integration and the effective use of innovative and technological learning methods in the classroom teaching process. When it comes to learning vocabulary in a foreign language and the number of words to be learned in a foreign language is high, it is thought that technological applications provide more effective learning. Chen et al. (2021) express that integrating educational games into language education is effective in improving students’ vocabulary acquisition, aligning with the idea of a broader shift towards digital literacy. In addition, Dewi (2023) highlights the modern shift towards the use of Quizlet for vocabulary learning, suggesting that the integration of digital tools into educational frameworks is important. The portability of laptops and smartphones has prompted the development of novel instructional methods that are thought to improve English language proficiency especially vocabulary learning ( Chaikovska and Zbaravska, 2020 ). With the help of this process, associating target words with visuals such as various graphics, pictures, images, cartoons, etc. is thought to benefit vocabulary learning by improving the cerebral schemas of foreign language vocabulary learners. Chaikovska and Zbaravska (2020) also state that associating unknown words with visuals, such as bright graphics and exaggerated pictures, benefits vocabulary acquisition. According to Andarab (2019) , using technology to contextualize vocabulary items during vocabulary acquisition improves the vocabulary learning process. This reinforcement of learning through visual aids and contextualization aligns with cognitive theories of multimedia learning, which posit that learners can more effectively process and retain information when it is presented in both verbal and visual formats. By suggesting that visual context plays an important role in memory and learning, it is suggested that visual context directs spatial attention, helps to realize implicit learning and can increase memory retention ( Chun and Jiang, 1998 ). The findings also highlight Quizlet’s usefulness in vocabulary learning and highlight the need of utilizing Quizlet to contextualize lexical items in collocations to improve vocabulary acquisition. Chaikovska and Zbaravska (2020) , while explaining the effect of Quizlet application on vocabulary learning, emphasized that the graphic presentation of the words in the program sets enriches cognitive visualization and can increase the level of word memorization by using the potential of the right hemisphere of the learners’ brain. In his study, Sanosi (2018) also highlights Quizlet’s potential in improving vocabulary learning. Sanosi (2018) asserts that Quizlet’s effectiveness as an e-learning tool for enhancing vocabulary acquisition can be linked to the increasing influence of information technology in many facets of life. The majority of daily duties for the younger generation of learners are completed on smart devices that are connected to the internet. Quizlet’s incorporation into daily technology use illustrates how learning and technology may coexist together and shows how relevant it is to the modern student’s digital habits. The principles of timed repetition and active recall, which support effective learning processes, form the foundation of Quizlet’s cognitive engagement, which is facilitated through repeated exploration and interactive quizzes.

The second research question addressed in this study focused on the effectiveness of the Quizlet on students’ vocabulary learning retention. A meta-analysis including five relevant research was carried out to provide an answer to this query. A homogeneity test was performed to determine the suitability of employing either the fixed effects model or the random effects model in the research. The results of the homogeneity test indicated a statistically significant difference, signifying a heterogeneous distribution of effect sizes among the studies ( Q  = 20.997; p  < 0.05). The mean of the effect sizes was calculated as 0.74 ( g  = 0.74). It was determined that the I 2 value obtained in the study showed heterogeneity with 80.947%. Since there was heterogeneity among the studies, effect sizes were calculated with the random effects model. According to the research findings, the average effect size indicated a moderate level of effectiveness in favor of the Quizlet. Quizlet has a moderate impact on vocabulary retention for those learning a foreign language. This impact can be attributed to several factors. The positive impact of Quizlet on retention can be attributed to the testing effect, which suggests that the act of quizzing helps learners identify knowledge gaps and actively seek out new information ( Karpicke and Roediger, 2008 ; Nguyen and Van Le, 2022 ). This finding illuminates the importance of Quizlet’s interactive features for retention of learnt information and the importance of engaging in retrieval practice. The theoretical basis for this effect can be attributed to the test effect, which suggests that retrieval practice increases long-term memory retention by engaging in continuous repetition. This principle underlines the importance of incorporating active retrieval techniques into learning strategies, especially for vocabulary retention. This theory is supported by research indicating that repeated testing produces a significant positive effect on delayed recall, compared to repeated studying after learning ( Karpicke and Roediger, 2008 ). Additionally, Nguyen et al. (2022) expressed that Quizlet creates motivation and arouses interest in learning within students’ consciousness, contributing to its impact on vocabulary retention. Moreover, the convenience and effectiveness of Quizlet, along with its features designed to be fun, make it appealing to students, thereby positively influencing vocabulary retention ( Aprilani and Suryaman, 2021 ; Pham, 2022 ). The fun and motivational aspects of Quizlet, along with its interactive and engaging design, support intrinsic motivation theories that emphasize the role of enjoyment and interest in sustaining learning engagement, achievement and retention. The impact of Quizlet on vocabulary retention can also be attributed to its ability to address prevalent problems among learners in the digital era, such as low participation and difficulties in maintaining learners’ attention to lessons ( Anjaniputra and Salsabila, 2018 ). Moreover, the incorporation of integrated skills and cognitive visualization in Quizlet makes it a useful ICT tool in vocabulary learning, contributing to its impact on vocabulary retention ( Chaikovska and Zbaravska, 2020 ). Dual coding theory, which enhances vocabulary retention by activating both verbal and nonverbal systems, is responsible for Quizlet’s effect on students’ success in vocabulary learning and retention ( Körlü and Mede, 2018 ). Quizlet’s effectiveness in increasing vocabulary retention through dual coding theory is thought to promote more robust encoding and retrieval of vocabulary by enhancing and strengthening the synergistic interaction between linguistic and visual information processing. Furthermore, it has been determined that Quizlet’s influence on students’ performance in vocabulary learning and retention is partially due to the dual coding theory (DCT) ( Körlü and Mede, 2018 ). According to the study’s participants, utilizing Quizlet gave them confidence that they had learned the vocabulary items and helped them rapidly and easily remember the new words they had learnt thanks to its study and fun aspects ( Körlü and Mede, 2018 ). This confidence and ease of recall provided by Quizlet can not only make and enhance the learning experience more effective, but can also contribute to a positive learning environment, in line with self-efficacy theory, which suggests that belief in one’s ability to succeed in certain situations or perform a task can significantly influence learning outcomes ( Laufer and Hulstijn, 2001 ). The application of Quizlet has been found to contribute to the development of linguistic intelligence, enriching students’ vocabulary banks and enhancing their vocabulary mastery, thereby impacting vocabulary retention ( Lubis et al., 2022 ). The use of Quizlet as a learning resource has also been recognized as an effort to develop the digital literacy of learners and motivate them to learn, further contributing to its impact on vocabulary retention ( Setiawan and Putro, 2021 ). The role of Quizlet in advancing digital literacy and linguistic intelligence underlines the multifaceted benefits of digital learning tools, suggesting that their impact extends beyond immediate learning outcomes to include broader educational and developmental gains. Research on the impact of visual features on vocabulary learning and retention ( Hashemi and Pourgharib, 2013 ) may provide an explanation for this discrepancy as it suggests that incorporating visual aids helps students remember and retain words more readily. On the contrary, there is also a study that supports that Quizlet is less effective in retention than traditional paper flashcards. In the study by Ashcroft et al. (2018) , the findings indicate that for delayed gains, there is an even stronger negative association between proficiency and Quizlet’s improved performance compared to paper flashcards. In actuality, advanced individuals lost their digital gains much more quickly than they did their paper gains. This contrast provides an opportunity to further investigate the conditions under which digital tools such as Quizlet optimize learning outcomes and highlights the importance of personalized and adaptive learning approaches that address learners’ different needs and proficiency levels.

The last problem of this study was to investigate the effectiveness of Quizlet on students’ attitude based on the findings of the studies. To find an answer to this problem, a meta-analysis of 2 studies was conducted. Homogeneity test was conducted to determine whether it is appropriate to use the fixed effects model or the random effects model in the research. According to the results of the homogeneity test, no difference was found, and it was concluded that the effect size distribution of the studies was homogeneous ( Q = 2.003; p > 0.05). It was determined that the I 2 value obtained in the study showed homogeneity with 50.081%. Since there was homogeneity among the studies, effect sizes were calculated with the fixed effects model. According to the fixed effects model, the average effect size of the studies included in the meta-analysis attitude was calculated as 0.37 ( g = 0.37). According to the research findings, the mean effect size value was found to be positive. The average effect size indicated a small level of effectiveness. This small but positive effect on attitudes towards language learning with Quizlet can be explained by the fact that digital tools can increase student engagement and motivation, but the magnitude of this effect can vary depending on factors such as implementation processes, student preferences and educational context. This variability requires a careful and detailed understanding of how digital tools such as Quizlet fit into the wider educational system and their role in shaping student attitudes and motivation. This also can be explained by the lack of quantitative studies measuring student attitudes towards the Quizlet application. The paucity of limited quantitative research on student attitudes towards Quizlet underlines the need for more robust empirical research that can offer deeper insights into how digital tools influence students’ psychological and emotional engagement in language learning. The lack of quantitative studies measuring student attitudes towards the Quizlet application is further supported by ( Mykytka, 2023 ), who highlighted the focus on vocabulary acquisition and the limited investigation of the effect of Quizlet on other skills. On the other hand, there are many qualitative studies proving that the Quizlet application increases student attitude and motivation positively ( Chien, 2015 ; Dizon, 2016 ; Alastuey and Nemeth, 2020 ; Setiawan and Wiedarti, 2020 ; Lubis et al., 2022 ; Nguyen et al., 2022 ; Pham, 2022 ; Zeitlin and Sadhak, 2022 ). Qualitative studies supporting the positive impact of Quizlet on student attitude and motivation emphasize the subjective and experiential dimensions of learning with digital tools and reveal that the effectiveness of these tools can be significantly affected by students’ perceptions and experiences. The effectiveness of Quizlet in increasing students’ attitude and motivation towards learning has been widely documented in the literature. The reasons for this positive influence can be attributed to various factors. Firstly, Quizlet has been shown to create a motivational learning environment by making the process of vocabulary acquisition more enjoyable and engaging for students and thus having positive impact on attitude ( Alastuey and Nemeth, 2020 ; Chaikovska and Zbaravska, 2020 ; Setiawan and Wiedarti, 2020 ; Aprilani and Suryaman, 2021 ; Berliani and Katemba, 2021 ; Mykytka, 2023 ). This enhancement of the learning environment through engagement and enjoyment reflects broader principles of educational psychology that emphasize the importance of positive emotional experiences in enhancing learning and student attitude. The interactive and gamified nature of Quizlet, such as its flashcards, quizzes, and other interactive activities, enhance students’ attitude, interest and intrinsic motivation in learning vocabulary ( Körlü and Mede, 2018 ; Alastuey and Nemeth, 2020 ; Nguyen et al., 2022 ; Mykytka, 2023 ). The gamification of learning processes facilitated by using Quizlet is also considered to be compatible with the principles of game-based learning, which suggest that game elements can significantly increase attitude and engagement and thus positively affect learning outcomes. Additionally, the convenience and effectiveness of Quizlet have been reported to positively influence students’ attitude, motivation and interest in vocabulary learning ( Pham, 2022 ; Zeitlin and Sadhak, 2022 ). This positive effect of Quizlet on student attitude and achievement demonstrates the importance of the role of user-friendly and effective digital tools in increasing student engagement and satisfaction in the learning process. And, Quizlet app’s wide range of activities and high degree of instant feedback, which paper flashcards could not match, may have increased and maintained students’ attitude engagement and motivation ( Ashcroft et al., 2018 ). In contrast to traditional learning methods, the immediate and fast feedback provided by Quizlet facilitates more effective learning by helping students to quickly identify and correct errors, which can be explained by the feedback loop theory, which suggests that timely and relevant feedback is crucial for learning, engagement and attitude. This theory is supported by the research which discusses the immediate feedback assessment technique and its role in promoting learning and correcting inaccurate first responses ( Epstein et al., 2002 ; Dihoff et al., 2004 ).

The current study demonstrates that Quizlet is an appropriate educational technology for fostering the learners’ cognitive and emotional dimensions in foreign learning process, especially in vocabulary learning. Apart from the technology tools and programs that aid in language acquisition, Quizlet has become a highly effective instrument for improving vocabulary knowledge and fostering learners’ attitude. After taking into account all of its benefits, Quizlet is an efficient web-based mobile learning tool that is entertaining, motivating, and helpful for learning vocabulary. Also, the design of the Quizlet application is suitable for autonomous learners, which enhances students’ attitude and motivation in learning vocabulary ( Setiawan and Wiedarti, 2020 ). This availability for autonomous learning reflects the growing demand for personalized and self-directed learning opportunities in modern education and highlights Quizlet’s role in meeting these evolving educational needs. The literature indicates that students’ opinions of Quizlet as a tool for vocabulary development were important in determining whether or not language learners should utilize it to increase their vocabulary. The importance and evaluation of learner views emphasizes the importance of learner-centered approaches in educational technology research and shows that the effectiveness of digital tools such as Quizlet can be significantly affected by learners’ achievement, learning retention, attitudes. Overall, the literature supports the importance of Quizlet in enhancing learners’ vocabulary learning, retention, and attitude, making it a valuable tool for educators and learners alike. This comprehensive perspective emphasizes the multifaceted impact of Quizlet on language learning, from learning achievement and retention to student attitudes, and underlines the need for its integration into language teaching practices. The study’s overall conclusions highlight the importance of incorporating mobile assisted language learning and teaching resources like Quizlet into teaching and learning practices and curricula. Quizlet was found to be a useful and effective application that supports students’ performance and autonomy in vocabulary learning by giving them increased exposure to the target words through a variety of functions and a study environment that is like a game. It is thought that the integration of Quizlet into language teaching, especially vocabulary teaching, could mean a shift towards more interactive, engaging and learner-centered approaches, reflecting the ongoing evolution of educational paradigms in the digital age.

6 Conclusion

This meta-analysis was conducted to investigate the effects of Quizlet on the cognitive and affective outcomes of foreign language learners, especially on vocabulary learning achievement, retention and attitude, and to reach a general conclusion on this issue. The findings of this study suggest that Quizlet has a moderate positive effect on vocabulary learning and retention and a small effect on learner attitude, suggesting that Quizlet may have the potential to be a valuable educational technology tool in language acquisition. The integration of Quizlet into the learning process not only facilitates students’ adaptation to modern technological tools, but also enhances their ability to effectively learn and retain large amounts of foreign vocabulary knowledge. This effectiveness can be partly attributed to Quizlet’s combination of visual aids and cognitive visualization techniques, which, as many studies have shown, play a crucial role in enhancing vocabulary acquisition and aiding retention. These visual components, coupled with the interactive nature of Quizlet, can help create a more engaging and immersive learning environment, which can be especially useful in the context of foreign language acquisition, especially in vocabulary learning, where visual associations can significantly support the learning process.

Despite these positive findings, our analysis also indicates a relatively smaller effect of Quizlet on learners’ attitudes towards vocabulary learning. This may be attributed to the limited number of quantitative studies specifically addressing this aspect of language learning. While existing qualitative research provides some evidence of Quizlet’s positive impact on learner motivation and attitude, there is a clear need for more rigorous, quantitative investigations to substantiate these observations. The discrepancy between qualitative and quantitative findings highlights a potential gap in the research, suggesting that future studies should aim to quantitatively measure and understand the nuances of how digital learning tools like Quizlet influence learners’ attitudes. Thanks to technological advances and the latest educational techniques, teachers are now able to use a wide range of online and mobile applications. The nuanced relationship between technology use and student attitude raises important questions about the adaptability and effectiveness of digital tools in different learning contexts. As digital learning environments continue to evolve, understanding these dynamics becomes increasingly important to optimize their design and implementation for maximum educational benefit. In light of these findings, it is clear that Quizlet shows considerable promise in improving vocabulary learning and retention but that further research is needed to fully understand its impact on student attitudes. Such insights can be important for educators and curriculum designers to make informed decisions about integrating digital tools such as Quizlet into language learning programs. The future of language education increasingly involves the integration of technology into educational processes. It is of utmost importance that such endeavors are developed and channeled in such a way that this integration contributes positively to student learning, achievement, attitudes and many other aspects.

In conclusion, while our study confirms the effectiveness of Quizlet in improving vocabulary learning, retention and learner attitude, it also highlights areas where further research is needed. Quizlet, with its interactive and engaging features, emerges as a valuable tool that facilitates the learning process and is effective and helpful in the learning processes of language educators and learners. It is thought that it may be important to integrate mobile assisted language learning resources such as Quizlet into educational practices and curricula as auxiliary tools to support foreign language learners’ performance in vocabulary acquisition and to improve their attitudes positively. This study may shed light and open new avenues for future research on how different aspects of Quizlet and similar platforms can be optimized for educational success.

7 Limitations and future research directions

7.1 quantitative research on learner attitudes.

A significant gap has been identified in quantitative research addressing the impact of Quizlet on students’ attitudes. Future studies should utilize robust quantitative methodologies to systematically assess how Quizlet affects student attitudes.

7.2 Temporal scope of studies

Longitudinal studies are recommended to examine the sustained impact of Quizlet on vocabulary learning over long periods of time. Such studies would provide invaluable insights into the long-term effectiveness and adaptability of Quizlet in evolving educational settings.

7.3 Comparative efficacy studies

Future research should take a more comprehensive approach, including a wider range of comparative analyses between Quizlet and both traditional and digital learning tools. Such comparative studies would deepen our understanding of Quizlet’s effectiveness relative to other methods and provide detailed insights into Quizlet’s unique advantages and areas for improvement.

7.4 Contextual diversity in learning environments

The majority of the studies reviewed focused on formal educational settings. There is a need for research exploring the use of Quizlet in more varied contexts, including informal learning environments and self-directed learning scenarios. Investigating Quizlet’s application in these diverse settings would offer a more holistic understanding of its adaptability and effectiveness across different learning modalities.

7.5 Technological advancements and evolving educational technologies

The rapid development of technology and its integration into educational contexts requires the continuous evaluation of tools such as Quizlet. Future studies should not only focus on Quizlet’s current functionalities, but also consider emerging technological developments that may affect its educational utility. Continuous evaluation is crucial to understand how evolving features and changes in user interaction with technology affect learning outcomes.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

OÖ: Writing – original draft. HS: Writing – review & editing.

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Note: References marked with an asterisk indicate studies included in the meta-analysis.

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Keywords: Quizlet, attitude, retention, achievement, meta-analysis, vocabulary learning, mobile assisted learning

Citation: Özdemir O and Seçkin H (2024) Quantifying cognitive and affective impacts of Quizlet on learning outcomes: a systematic review and comprehensive meta-analysis. Front. Psychol . 15:1349835. doi: 10.3389/fpsyg.2024.1349835

Received: 05 December 2023; Accepted: 16 February 2024; Published: 06 March 2024.

Reviewed by:

Copyright © 2024 Özdemir and Seçkin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Osman Özdemir, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Home > Blog > Tips for Online Students > The Ultimate Student Guide To Finding Credible Sources

Tips for Online Students , Tips for Students

The Ultimate Student Guide To Finding Credible Sources

Updated: June 19, 2024

Published: January 1, 2020

When it comes to writing a research paper, it’s crucial that you use credible sources to make sure that the information you are stating is actually true. Knowing the difference between credible sources and unreliable sources doesn’t always come so easily with endless information flooding the internet. Thankfully, there are some simple tips that you can use to ensure that you are always using credible sources for research.

What is a Research Paper?

A research paper is a piece of academic writing that uses original research on a specific topic. There are many different types of research papers, ranging from a high school term paper to a master’s thesis or doctoral dissertation.

Photo by  Wallace Chuck  from  Pexels

How to start a search for sources, 1. start simple.

If you’re wondering how to find sources for a research paper, the easiest and best way to start is simple! Just try browsing through some common search engines to see what you find.

2. Cross Wikipedia off

Wikipedia, although it’s a massive pool of information, should always be avoided when writing a research paper since it allows the public to edit information. Sites such as these often run the risk of lacking accuracy, and is not one of the most credible sources for research.

3. Yes to scholarly databases

Scholarly databases are your best friend when it comes to finding credible sources for research. Online scholarly databases that can be trusted and are known to provide useful information for students include LexisNexis and EBSCO.

4. Newspapers and magazines

Although sometimes biased, newspapers and magazines can also be a great place to find information about current events.

5. The library

While the library seems to be the most obvious place to find information, somehow it’s often forgotten when it comes to research in the modern age. Don’t forget how useful it can truly be!

Types of Credible Sources for Research

1. what are some credible websites.

Many online sources do not necessarily contain information that is correct or has been checked. That’s why it’s of utmost importance to make sure that you’re using the right websites for your research, with government and educational websites generally being the most reliable.

Credible sources for research include: science.gov, The World Factbook, US Census Bureau, UK Statistics, and Encyclopedia Britannica.

2. What are some credible journal articles?

When it comes to journal articles, determining how credible they are comes much easier than other sources. This is generally due to the fact that many of these websites will include valuable information such as how many times the article has been cited, and if its been peer reviewed.

Some great examples of reliable websites for journal articles include Google Scholar, Oxford Academic, Microsoft Academic, Cornell University Library, and SAGE Publishing.

If you are ever not sure how to find credible sources, then there’s the CRAAP test, which takes into account the Currency, Relevance, Authority, Accuracy and Purpose of the article. Take all of these factors into consideration before using a source and determining whether or not it’s credible enough. Even if it takes more time, you’ll be saving yourself tons of time in the long run by not using unreliable sources.

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3. what are some credible news sources.

When it comes to news articles, more caution must be taken since it’s hard to know which sources are truly reliable and unbiased. The CRAAP test is also useful in this type of article for research.

A few examples of credible news sources include The New York Times, Bloomberg, and The Washington Post.

The Credibility of a Source

As you search for your research information, you will surely come across the question of how to find credible sources for a research paper. Here are some criteria to focus on to ensure that you only use the most credible of sources.

1. What’s the depth of it?

Always look at the depth of an article, not just the written content. See how long the article is, and if it contains the necessary information such as an abstract, a reference list, and documented data.

2. Who is reading it?

When judging the credibility of an article, it’s important to always ask yourself who the target audience of the article is. Sometimes, sources have a specific goal in mind and it can create certain biases.

3. What’s the goal?

Just as you should do with the audience, also ask yourself what the article is trying to achieve. What is their ultimate goal and how are they persuading you of that?

4. Who wrote it?

Always ask yourself who wrote the article and how reputable they are in the specific field. Look at what other published works they have as well.

5. Can it be trusted?

Overall, it’s key to ask yourself how reputable the source is. What kind of website is it published on? Look at the big picture.

6. Is it relevant to now?

Look at the date of the article, or about the specific things they are mentioning in the article. If it’s from a few years ago, it’s probably not too relevant to your current research.

7. Can it be proven?

While an article may sound incredibly convincing, many people have a way with words and persuasion. Stop and ask yourself whether or not what they are claiming can actually be proven.

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How to evaluate source credibility.

By using unreliable sources in your research, it can discredit your status, which is why it’s incredibly important to make sure that any information you are using is up-to-date and accurate.

Here’s how to find credible sources.

1. What is a credible source?

Generally, materials that have been published within the past 10 years are considered to be credible sources for research. Another important factor to consider is the author — if they are well known and respected in their specific fields, that’s also generally a sign that the article is credible. Educational and government-run websites (.gov, .edu) tend to also be a safe source to use, as well as academic databases. Google Scholar is also a no-fail source for reliable information.

2. What is a potentially unreliable source?

Anything that is out of date, meaning it’s been published more than 10 years ago should be avoided. Materials published on social media platforms such as Facebook or personal blogs don’t tend to be the most credible. Always make sure that an article contains proper citations and that the website you are using ends in .com or .org.

Free Resources For Learning

There are many free resources for research available known as open educational resources . They are licensed for free use, with the intention of teaching. They can be determined as credible sources for research if they have a Creative Common license, and if the author has proven to be an expert in their field. Always make sure that the content you are using contains no biases.

Sites For Scholarly Research

When performing scholarly research, it’s extra important to make sure that your sources are credible. Government-run research is considered credible, but beware of any political sites. University and educational websites also tend to be reliable, but still take everything you read with a grain of salt. Company websites also tend to be reliable, although their ultimate goal is usually to promote a product. Organizations which are .org websites can be professional and reliable, however, sometimes they also have their own interests.

Which Sites Can Be Relied On

The internet has no shortage of information out there. That’s why you’ll need these handy tips to determine which to use, and how to distinguish through the vast choices without feeling overwhelmed.

List of Credible Research Sources to Consider

1. government entities.

These websites tend to be reliable since they are highly regulated. Examples include the CIA World Factbook and the United States Justice Statistics.

2. Research Think Tanks

Examples of reliable research think tanks include Rand Corporation, Pew Research Center and The Milken Institute.

3. Academic Libraries and Databases

ProQuest, Scopus, and Jstor are great examples of academic libraries and databases that can be trusted.

4. Professional Standards Organizations

The American Bar Association and The American Psychological Association (APA) are highly credible sources when it comes to professional standards.

How to Write a Research Paper: Step-by-Step

Now that you’re an expert on finding credible sources for research, you’re ready to go! But how do you even start to write a research paper? Don’t worry, we’ve got you covered.

For starters, it’s important to get clear instructions from your professor on what they want. The next step is to start brainstorming ideas for a topic of research. Once you’ve decided and feel confident about it, you’re ready to create your outline and plan out the goal of your research paper.

Befriend your librarian and start to search for quality and credible sources through a variety of means. Make sure you understand your topic from top to bottom before you start writing.  As you write, be sure to always keep things factual, and that you finalize your thesis statement throughout your paper — not just at the end. That’s what’s going to guide your writing. Be sure to always keep format in mind, never forget to cite your sources, and to never skip those edits and final checks.

Now you are ready to write a high-quality, fact-driven research paper that’s sure to impress your professors.

In this article

At UoPeople, our blog writers are thinkers, researchers, and experts dedicated to curating articles relevant to our mission: making higher education accessible to everyone. Read More

• USC Libraries
• Research Guides

Organizing Your Social Sciences Research Paper

• Reading Research Effectively
• Purpose of Guide
• Design Flaws to Avoid
• Independent and Dependent Variables
• Glossary of Research Terms
• Narrowing a Topic Idea
• Broadening a Topic Idea
• Extending the Timeliness of a Topic Idea
• Academic Writing Style
• Applying Critical Thinking
• Choosing a Title
• Making an Outline
• Paragraph Development
• Research Process Video Series
• Executive Summary
• The C.A.R.S. Model
• Background Information
• The Research Problem/Question
• Theoretical Framework
• Citation Tracking
• Content Alert Services
• Evaluating Sources
• Primary Sources
• Secondary Sources
• Tiertiary Sources
• Scholarly vs. Popular Publications
• Qualitative Methods
• Quantitative Methods
• Insiderness
• Using Non-Textual Elements
• Limitations of the Study
• Common Grammar Mistakes
• Writing Concisely
• Avoiding Plagiarism
• Footnotes or Endnotes?
• Further Readings
• Generative AI and Writing
• USC Libraries Tutorials and Other Guides
• Bibliography

Reading a Scholarly Article or Research Paper

Identifying a research problem to investigate requires a preliminary search for and critical review of the literature in order to gain an understanding about how scholars have examined a topic. Scholars rarely structure research studies in a way that can be followed like a story; they are complex and detail-intensive and often written in a descriptive and conclusive narrative form. However, in the social and behavioral sciences, journal articles and stand-alone research reports are generally organized in a consistent format that makes it easier to compare and contrast studies and interpret their findings.

General Reading Strategies

W hen you first read an article or research paper, focus on asking specific questions about each section. This strategy can help with overall comprehension and with understanding how the content relates [or does not relate] to the problem you want to investigate. As you review more and more studies, the process of understanding and critically evaluating the research will become easier because the content of what you review will begin to coalescence around common themes and patterns of analysis. Below are recommendations on how to read each section of a research paper effectively. Note that the sections to read are out of order from how you will find them organized in a journal article or research paper.

1.  Abstract

The abstract summarizes the background, methods, results, discussion, and conclusions of a scholarly article or research paper. Use the abstract to filter out sources that may have appeared useful when you began searching for information but, in reality, are not relevant. Questions to consider when reading the abstract are:

• Is this study related to my question or area of research?
• What is this study about and why is it being done ?
• What is the working hypothesis or underlying thesis?
• What is the primary finding of the study?
• Are there words or terminology that I can use to either narrow or broaden the parameters of my search for more information?

2.  Introduction

If, after reading the abstract, you believe the paper may be useful, focus on examining the research problem and identifying the questions the author is trying to address. This information is usually located within the first few paragraphs of the introduction or in the concluding paragraph. Look for information about how and in what way this relates to what you are investigating. In addition to the research problem, the introduction should provide the main argument and theoretical framework of the study and, in the last paragraphs of the introduction, describe what the author(s) intend to accomplish. Questions to consider when reading the introduction include:

• What is this study trying to prove or disprove?
• What is the author(s) trying to test or demonstrate?
• What do we already know about this topic and what gaps does this study try to fill or contribute a new understanding to the research problem?
• Why should I care about what is being investigated?
• Will this study tell me anything new related to the research problem I am investigating?

3.  Literature Review

The literature review describes and critically evaluates what is already known about a topic. Read the literature review to obtain a big picture perspective about how the topic has been studied and to begin the process of seeing where your potential study fits within the domain of prior research. Questions to consider when reading the literature review include:

• W hat other research has been conducted about this topic and what are the main themes that have emerged?
• What does prior research reveal about what is already known about the topic and what remains to be discovered?
• What have been the most important past findings about the research problem?
• How has prior research led the author(s) to conduct this particular study?
• Is there any prior research that is unique or groundbreaking?
• Are there any studies I could use as a model for designing and organizing my own study?

4.  Discussion/Conclusion

The discussion and conclusion are usually the last two sections of text in a scholarly article or research report. They reveal how the author(s) interpreted the findings of their research and presented recommendations or courses of action based on those findings. Often in the conclusion, the author(s) highlight recommendations for further research that can be used to develop your own study. Questions to consider when reading the discussion and conclusion sections include:

• What is the overall meaning of the study and why is this important? [i.e., how have the author(s) addressed the " So What? " question].
• What do you find to be the most important ways that the findings have been interpreted?
• What are the weaknesses in their argument?
• Do you believe conclusions about the significance of the study and its findings are valid?
• What limitations of the study do the author(s) describe and how might this help formulate my own research?
• Does the conclusion contain any recommendations for future research?

5.  Methods/Methodology

The methods section describes the materials, techniques, and procedures for gathering information used to examine the research problem. If what you have read so far closely supports your understanding of the topic, then move on to examining how the author(s) gathered information during the research process. Questions to consider when reading the methods section include:

• Did the study use qualitative [based on interviews, observations, content analysis], quantitative [based on statistical analysis], or a mixed-methods approach to examining the research problem?
• What was the type of information or data used?
• Could this method of analysis be repeated and can I adopt the same approach?
• Is enough information available to repeat the study or should new data be found to expand or improve understanding of the research problem?

6.  Results

After reading the above sections, you should have a clear understanding of the general findings of the study. Therefore, read the results section to identify how key findings were discussed in relation to the research problem. If any non-textual elements [e.g., graphs, charts, tables, etc.] are confusing, focus on the explanations about them in the text. Questions to consider when reading the results section include:

• W hat did the author(s) find and how did they find it?
• Does the author(s) highlight any findings as most significant?
• Are the results presented in a factual and unbiased way?
• Does the analysis of results in the discussion section agree with how the results are presented?
• Is all the data present and did the author(s) adequately address gaps?
• What conclusions do you formulate from this data and does it match with the author's conclusions?

7.  References

The references list the sources used by the author(s) to document what prior research and information was used when conducting the study. After reviewing the article or research paper, use the references to identify additional sources of information on the topic and to examine critically how these sources supported the overall research agenda. Questions to consider when reading the references include:

• Do the sources cited by the author(s) reflect a diversity of disciplinary viewpoints, i.e., are the sources all from a particular field of study or do the sources reflect multiple areas of study?
• Are there any unique or interesting sources that could be incorporated into my study?
• What other authors are respected in this field, i.e., who has multiple works cited or is cited most often by others?
• What other research should I review to clarify any remaining issues or that I need more information about?

NOTE:   A final strategy in reviewing research is to copy and paste the title of the source [journal article, book, research report] into Google Scholar . If it appears, look for a "cited by" reference followed by a hyperlinked number under the record [e.g., Cited by 45]. This number indicates how many times the study has been subsequently cited in other, more recently published works. This strategy, known as citation tracking, can be an effective means of expanding your review of pertinent literature based on a study you have found useful and how scholars have cited it. The same strategies described above can be applied to reading articles you find in the list of cited by references.

Reading Tip

Specific Reading Strategies

Effectively reading scholarly research is an acquired skill that involves attention to detail and an ability to comprehend complex ideas, data, and theoretical concepts in a way that applies logically to the research problem you are investigating. Here are some specific reading strategies to consider.

As You are Reading

• Focus on information that is most relevant to the research problem; skim over the other parts.
• As noted above, read content out of order! This isn't a novel; you want to start with the spoiler to quickly assess the relevance of the study.
• Think critically about what you read and seek to build your own arguments; not everything may be entirely valid, examined effectively, or thoroughly investigated.
• Look up the definitions of unfamiliar words, concepts, or terminology. A good scholarly source is Credo Reference .

Taking notes as you read will save time when you go back to examine your sources. Here are some suggestions:

• Mark or highlight important text as you read [e.g., you can use the highlight text  feature in a PDF document]
• Take notes in the margins [e.g., Adobe Reader offers pop-up sticky notes].
• Highlight important quotations; consider using different highlighting colors to differentiate between quotes and other types of important text.
• Summarize key points about the study at the end of the paper. To save time, these can be in the form of a concise bulleted list of statements [e.g., intro provides useful historical background; lit review has important sources; good conclusions].

Write down thoughts that come to mind that may help clarify your understanding of the research problem. Here are some examples of questions to ask yourself:

• Do I understand all of the terminology and key concepts?
• Do I understand the parts of this study most relevant to my topic?
• What specific problem does the research address and why is it important?
• Are there any issues or perspectives the author(s) did not consider?
• Do I have any reason to question the validity or reliability of this research?
• How do the findings relate to my research interests and to other works which I have read?

Adapted from text originally created by Holly Burt, Behavioral Sciences Librarian, USC Libraries, April 2018.

Another Reading Tip

When is it Important to Read the Entire Article or Research Paper

Laubepin argues, "Very few articles in a field are so important that every word needs to be read carefully." * However, this implies that some studies are worth reading carefully if they directly relate to understanding the research problem. As arduous as it may seem, there are valid reasons for reading a study from beginning to end. Here are some examples:

• Studies Published Very Recently .  The author(s) of a recent, well written study will provide a survey of the most important or impactful prior research in the literature review section. This can establish an understanding of how scholars in the past addressed the research problem. In addition, the most recently published sources will highlight what is known and what gaps in understanding currently exist about a topic, usually in the form of the need for further research in the conclusion .
• Surveys of the Research Problem .  Some papers provide a comprehensive analytical overview of the research problem. Reading this type of study can help you understand underlying issues and discover why scholars have chosen to investigate the topic. This is particularly important if the study was published recently because the author(s) should cite all or most of the important prior research on the topic. Note that, if it is a long-standing problem, there may be studies that specifically review the literature to identify gaps that remain. These studies often include the word "review" in their title [e.g., Hügel, Stephan, and Anna R. Davies. "Public Participation, Engagement, and Climate Change Adaptation: A Review of the Research Literature." Wiley Interdisciplinary Reviews: Climate Change 11 (July-August 2020): https://doi.org/10.1002/ wcc.645].
• Highly Cited .  If you keep coming across the same citation to a study while you are reviewing the literature, this implies it was foundational in establishing an understanding of the research problem or the study had a significant impact within the literature [either positive or negative]. Carefully reading a highly cited source can help you understand how the topic emerged and how it motivated scholars to further investigate the problem. It also could be a study you need to cite as foundational in your own paper to demonstrate to the reader that you understand the roots of the problem.
• Historical Overview .  Knowing the historical background of a research problem may not be the focus of your analysis. Nevertheless, carefully reading a study that provides a thorough description and analysis of the history behind an event, issue, or phenomenon can add important context to understanding the topic and what aspect of the problem you may want to examine further.
• Innovative Methodological Design .  Some studies are significant and should be read in their entirety because the author(s) designed a unique or innovative approach to researching the problem. This may justify reading the entire study because it can motivate you to think creatively about also pursuing an alternative or non-traditional approach to examining your topic of interest. These types of studies are generally easy to identify because they are often cited in others works because of their unique approach to examining the research problem.
• Cross-disciplinary Approach .  R eviewing studies produced outside of your discipline is an essential component of investigating research problems in the social and behavioral sciences. Consider reading a study that was conducted by author(s) based in a different discipline [e.g., an anthropologist studying political cultures; a study of hiring practices in companies published in a sociology journal]. This approach can generate a new understanding or a unique perspective about the topic . If you are not sure how to search for studies published in a discipline outside of your major or of the course you are taking, contact a librarian for assistance.

* Laubepin, Frederique. How to Read (and Understand) a Social Science Journal Article . Inter-University Consortium for Political and Social Research (ISPSR), 2013

Shon, Phillip Chong Ho. How to Read Journal Articles in the Social Sciences: A Very Practical Guide for Students . 2nd edition. Thousand Oaks, CA: Sage, 2015; Lockhart, Tara, and Mary Soliday. "The Critical Place of Reading in Writing Transfer (and Beyond): A Report of Student Experiences." Pedagogy 16 (2016): 23-37; Maguire, Moira, Ann Everitt Reynolds, and Brid Delahunt. "Reading to Be: The Role of Academic Reading in Emergent Academic and Professional Student Identities." Journal of University Teaching and Learning Practice 17 (2020): 5-12.

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• Evaluating Sources | Methods & Examples

Evaluating Sources | Methods & Examples

Published on June 2, 2022 by Eoghan Ryan . Revised on May 31, 2023.

The sources you use are an important component of your research. It’s important to evaluate the sources you’re considering using, in order to:

• Ensure that they’re credible
• Determine whether they’re relevant to your topic
• Assess the quality of their arguments

Table of contents

Evaluating a source’s credibility, evaluating a source’s relevance, evaluating a source’s arguments, other interesting articles, frequently asked questions about evaluating sources.

Evaluating the credibility of a source is an important way of sifting out misinformation and determining whether you should use it in your research. Useful approaches include the CRAAP test and lateral reading .

One of the best ways to evaluate source credibility is the CRAAP test . This stands for:

• Currency: Does the source reflect recent research?
• Relevance: Is the source related to your research topic?
• Authority: Is it a respected publication? Is the author an expert in their field?
• Accuracy: Does the source support its arguments and conclusions with evidence?
• Purpose: What is the author’s intention?

How you evaluate a source using these criteria will depend on your subject and focus. It’s important to understand the types of sources and how you should use them in your field of research.

Lateral reading

Lateral reading is the act of evaluating the credibility of a source by comparing it to other sources. This allows you to:

• Verify evidence
• Contextualize information
• Find potential weaknesses

If a source is using methods or drawing conclusions that are incompatible with other research in its field, it may not be reliable.

Rather than taking these figures at face value, you decide to determine the accuracy of the source’s claims by cross-checking them with official statistics such as census reports and figures compiled by the Department of Homeland Security’s Office of Immigration Statistics.

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How you evaluate the relevance of a source will depend on your topic, and on where you are in the research process . Preliminary evaluation helps you to pick out relevant sources in your search, while in-depth evaluation allows you to understand how they’re related.

Preliminary evaluation

As you cannot possibly read every source related to your topic, you can use preliminary evaluation to determine which sources might be relevant. This is especially important when you’re surveying a large number of sources (e.g., in a literature review or systematic review ).

One way to do this is to look at paratextual material, or the parts of a work other than the text itself.

• Look at the table of contents to determine the scope of the work.
• Consult the index for key terms or the names of important scholars.

You can also read abstracts , prefaces , introductions , and conclusions . These will give you a clear idea of the author’s intentions, the parameters of the research, and even the conclusions they draw.

Preliminary evaluation is useful as it allows you to:

• Determine whether a source is worth examining in more depth
• Quickly move on to more relevant sources
• Increase the quality of the information you consume

While this preliminary evaluation is an important step in the research process, you should engage with sources more deeply in order to adequately understand them.

In-depth evaluation

Begin your in-depth evaluation with any landmark studies in your field of research, or with sources that you’re sure are related to your research topic.

As you read, try to understand the connections between the sources. Look for:

• Key debates: What topics or questions are currently influencing research? How does the source respond to these key debates?
• Major publications or critics: Are there any specific texts or scholars that have greatly influenced the field? How does the source engage with them?
• Trends: Is the field currently dominated by particular theories or research methods ? How does the source respond to these?
• Gaps: Are there any oversights or weaknesses in the research?

Even sources whose conclusions you disagree with can be relevant, as they can strengthen your argument by offering alternative perspectives.

Every source should contribute to the debate about its topic by taking a clear position. This position and the conclusions the author comes to should be supported by evidence from direct observation or from other sources.

Most sources will use a mix of primary and secondary sources to form an argument . It is important to consider how the author uses these sources. A good argument should be based on analysis and critique, and there should be a logical relationship between evidence and conclusions.

To assess an argument’s strengths and weaknesses, ask:

• Does the evidence support the claim?
• How does the author use evidence? What theories, methods, or models do they use?
• Could the evidence be used to draw other conclusions? Can it be interpreted differently?
• How does the author situate their argument in the field? Do they agree or disagree with other scholars? Do they confirm or challenge established knowledge?

Situating a source in relation to other sources ( lateral reading ) can help you determine whether the author’s arguments and conclusions are reliable and how you will respond to them in your own writing.

If you want to know more about ChatGPT, AI tools , citation , and plagiarism , make sure to check out some of our other articles with explanations and examples.

• ChatGPT vs human editor
• ChatGPT citations
• Is ChatGPT trustworthy?
• Using ChatGPT for your studies
• What is ChatGPT?
• Chicago style
• Paraphrasing

 Plagiarism

• Types of plagiarism
• Self-plagiarism
• Avoiding plagiarism
• Academic integrity
• Consequences of plagiarism
• Common knowledge

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As you cannot possibly read every source related to your topic, it’s important to evaluate sources to assess their relevance. Use preliminary evaluation to determine whether a source is worth examining in more depth.

This involves:

• Reading abstracts , prefaces, introductions , and conclusions
• Looking at the table of contents to determine the scope of the work
• Consulting the index for key terms or the names of important scholars

Lateral reading is the act of evaluating the credibility of a source by comparing it with other sources. This allows you to:

A credible source should pass the CRAAP test  and follow these guidelines:

• The information should be up to date and current.
• The author and publication should be a trusted authority on the subject you are researching.
• The sources the author cited should be easy to find, clear, and unbiased.
• For a web source, the URL and layout should signify that it is trustworthy.

The CRAAP test is an acronym to help you evaluate the credibility of a source you are considering using. It is an important component of information literacy .

The CRAAP test has five main components:

• Currency: Is the source up to date?
• Relevance: Is the source relevant to your research?
• Authority: Where is the source published? Who is the author? Are they considered reputable and trustworthy in their field?
• Accuracy: Is the source supported by evidence? Are the claims cited correctly?
• Purpose: What was the motive behind publishing this source?

Scholarly sources are written by experts in their field and are typically subjected to peer review . They are intended for a scholarly audience, include a full bibliography, and use scholarly or technical language. For these reasons, they are typically considered credible sources .

Popular sources like magazines and news articles are typically written by journalists. These types of sources usually don’t include a bibliography and are written for a popular, rather than academic, audience. They are not always reliable and may be written from a biased or uninformed perspective, but they can still be cited in some contexts.

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• v.9(31); 2021 Nov 6

Major depressive disorder: Validated treatments and future challenges

Rabie karrouri.

Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, Fez 30070, Morocco

Zakaria Hammani

Roukaya benjelloun.

Department of Psychiatry, Faculty of Medicine, Mohammed VI University of Health Sciences, Casablanca 20000, Morocco

Yassine Otheman

Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, Fez 30070, Morocco. [email protected]

Corresponding author: Yassine Otheman, MD, Associate Professor, Chief Doctor, Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, 1893, Km 2.2 road of Sidi Hrazem, Fez 30070, Morocco. [email protected]

Depression is a prevalent psychiatric disorder that often leads to poor quality of life and impaired functioning. Treatment during the acute phase of a major depressive episode aims to help the patient reach a remission state and eventually return to their baseline level of functioning. Pharmacotherapy, especially selective serotonin reuptake inhibitors antidepressants, remains the most frequent option for treating depression during the acute phase, while other promising pharmacological options are still competing for the attention of practitioners. Depression-focused psychotherapy is the second most common option for helping patients overcome the acute phase, maintain remission, and prevent relapses. Electroconvulsive therapy is the most effective somatic therapy for depression in some specific situations; meanwhile, other methods have limits, and their specific indications are still being studied. Combining medications, psychotherapy, and somatic therapies remains the most effective way to manage resistant forms of depression.

Core Tip: Depression is a persistent public health problem for which treatments must be codified and simplified to enhance current practice. Several therapies have been suggested worldwide, with varying levels of validity. This article explores effective and valid therapies for treating depression by addressing current and future research topics for different treatment categories.

INTRODUCTION

Depression is a common psychiatric disorder and a major contributor to the global burden of diseases. According to the World Health Organization, depression is the second-leading cause of disability in the world and is projected to rank first by 2030[ 1 ]. Depression is also associated with high rates of suicidal behavior and mortality[ 2 ].

Treatments administered during the acute phase of a major depressive episode aim to help the patient reach a remission state and eventually return to their baseline level of functioning[ 3 ]. Acute-phase treatment options include pharmacotherapy, depression-focused psychotherapy, combinations of medications and psychotherapy, and somatic therapies such as electroconvulsive therapy (ECT). Nevertheless, managing the acute phase of depression is only the first step in a long therapy process that aims to maintain remission and prevent relapses. In this article, we discuss various treatment options implemented by clinicians, highlighting the role that each option plays in actual psychiatric practice.

PHARMACOTHERAPY

While selective serotonin reuptake inhibitors (SSRIs) remain the gold-standard treatment for depression, new antidepressants are always being developed and tested. The ultimate goal is to discover a molecule that exhibits quick effectiveness with as few side effects as possible.

Daniel Bovet studied the structure of histamine (the causative agent in allergic responses) to find an antagonist, which was finally synthesized in 1937[ 4 ]. Since then, many researchers have studied the link between the structures and activities of different antihistaminic agents, contributing to the discovery of almost all antidepressants[ 5 ].

In the following subsections, we list the main classes of antidepressants in chronological order of apparition, highlighting the most widely used molecules in daily psychiatric practice.

Monoamine oxidase inhibitors

Iproniazid was the first drug defined as an antidepressant; it was later classified as a monoamine oxidase inhibitor (MAOI)[ 6 , 7 ]. Several other MAOIs have been introduced since 1957[ 8 ]. Due to their irreversible inhibition of monoamine oxidase, MOAIs have numerous side effects, such as hepatotoxicity and hypertensive crises, that can lead to lethal intracranial hemorrhages. Consequently, MAOIs have become less commonly used over time[ 9 ].

Trials have demonstrated that MAOIs’ efficacy is comparable to that of tricyclic antidepressants (TCAs)[ 10 , 11 ]. However, considering MAOIs’ drug interactions, dietary restrictions, and potentially dangerous side effects, they are now almost exclusively prescribed for patients who have not responded to several other pharmacotherapies, including TCAs[ 9 ]. Furthermore, MAOIs have demonstrated specific efficacy in treating depression with atypical features, such as reactive moods, reverse neuro-vegetative symptoms, and sensitivity to rejection[ 12 ].

MAOIs are also a potential therapeutic option when ECT is contraindicated[ 13 ]. MAOIs’ effectiveness is still unclear for treating depression in patients who are resistant to multiple sequential trials with SSRIs and serotonin-norepinephrine reuptake inhibitors (SNRIs)[ 14 ]. Nevertheless, psychiatrists’ use of MAOIs has declined over the years[ 15 , 16 ]. The use of MAOIs is generally restricted to patients who do not respond to other treatments.

The first TCA was discovered and released for clinical use in 1957 under the brand name Tofranil[ 5 , 17 ]. Since then, TCAs have remained among the most frequently prescribed drugs worldwide[ 9 ]. TCAs-such as amitriptyline, nortriptyline, protriptyline, imipramine, desipramine, doxepin, and trimipramine-are about as effective as other classes of antidepressants-including SSRIs, SNRIs, and MAOIs-in treating major depression[ 18 , 19 ].

However, some TCAs can be more effective than SSRIs when used to treat hospitalized patients[ 20 ]. This efficacy can be explained by the superiority of TCAs over SSRIs for patients with severe major depressive disorder (MDD) symptoms who require hospitalization[ 21 - 24 ]. However, no differences have been detected in outpatients who are considered less severely ill[ 18 , 20 ]. In most cases, TCAs should generally be reserved for situations when first-line drug treatments have failed[ 25 ].

In December 1987, a series of clinical studies confirmed that an SSRI called fluoxetine was as effective as TCAs for treating depression while causing fewer adverse effects[ 26 ]. After being released onto the market, its use expanded more quickly than that of any other psychotropic in history. In 1994, it was the second-best-selling drug in the world[ 7 ].

Currently available SSRIs include fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram, and escitalopram. They have elicited different tolerance rates and side effects-mostly sexual and digestive (nausea and loss of appetite), as well as irritability, anxiety, insomnia, and headaches[ 27 ]. Nevertheless, SSRIs have a good tolerability profile[ 28 ].

In most systematic reviews and meta-analyses, SSRIs have demonstrated comparable efficacy to TCAs[ 18 , 19 , 29 ], and there is no significant evidence indicating the superiority of any other class or agent over SSRIs[ 29 - 31 ]. Furthermore, studies show no differences in efficacy among individual SSRIs[ 29 , 31 - 34 ]. Therefore, most guidelines currently recommend SSRIs as the first-line treatment for patients with major depression[ 25 ].

Norepinephrine reuptake inhibitors

Other monoamine (norepinephrine, serotonin, and dopamine) neurotransmitter reuptake inhibitors called SNRIs emerged during the 1990s to protect patients against the adverse effects of SSRIs[ 35 ]. Currently available SNRIs are venlafaxine, desvenlafaxine (the principal metabolite of venlafaxine), and duloxetine. The extended-release form of venlafaxine is the most commonly used drug in this class. Clinical guidelines commonly recommend prescribing SNRI to patients who do not respond to SSRIs[ 25 ].

In individual studies, venlafaxine and duloxetine are generally considered effective as SSRIs[ 36 ]. Also, venlafaxine’s efficacy is comparable to that of TCAs[ 37 , 38 ].

According to some meta-analyses, reboxetine (a selective noradrenaline reuptake inhibitor) seems less efficacious than SSRIs[ 39 ]. However, these findings could be due to the relatively poor tolerance of reboxetine[ 40 ].

Other antidepressants

Trazodone is the oldest medication of the so-called “other antidepressants” group that is still in wide use[ 41 , 42 ]. It has been shown to be an effective antidepressant in placebo-controlled research. However, in contemporary practice, it is much more likely to be used in low doses as a sedative-hypnotic than as an antidepressant[ 41 , 42 ].

Nefazodone’s structure is analogous to that of trazodone, though it has different pharmacological properties[ 43 ]. Its efficacy and overall tolerability are comparable to those of SSRIs, as indicated by comparative trials[ 43 ]. However, its use is associated with rare (but fatal) cases of clinical idiosyncratic hepatotoxicity[ 44 ].

Bupropion’s mechanism of action remains unclear, though it is classified as a norepinephrine and dopamine reuptake inhibitor[ 45 ]. It appears to have a more activating profile than SSRIs that are modestly superior to bupropion in patients with MDD[ 46 ]. However, for individuals with low to moderate levels of anxiety, the efficacy of bupropion in treating MDD is comparable to that of SSRIs[ 46 ]. Moreover, bupropion has a better tolerability profile than SSRIs, with minimal weight gain (or even leading to weight loss)[ 46 ]. In addition, bupropion is more likely than some SSRIs to improve symptoms of fatigue and sleepiness[ 47 ].

Mirtazapine and mianserin are tetracyclic compounds believed to increase the availability of serotonin or norepinephrine (or both), at least initially. Mirtazapine’s ability to antagonize serotoninergic subtypes receptors, <5-HT2A> and <5-HT2C>, could also increase norepinephrine and dopamine release in cortical regions[ 25 ]. Mirtazapine is about as effective as SSRIs[ 48 ].

Recently, drugs have been developed that block serotonin reuptake while affecting a variety of 5-HT receptor subtypes. The advantages of these agents ( e.g. , vilazodone and vortioxetine) over SSRIs are not fully clear. However, they appear to produce less sexual dysfunction and, in the specific case of vortioxetine, have particular benefits in depression-related cognitive impairment[ 49 ]. Indeed, vortioxetine is a very recent antidepressant with a multimodal mechanism that is thought to have a high affinity for serotonin transporters and 5-HT3, 5HT1A, 5HT7 receptors. Such a specific profile seems to indicate a level of efficacy to other antidepressants with a specific action on cognitive impairments[ 50 , 51 ].

In conclusion, no significant differences have been found between different classes of antidepressants in terms of their efficacy[ 52 ], though some drugs show some weak-to-moderate evidence indicating they are more effective than some other drugs[ 53 ]. Concerning the acceptability of these drugs, citalopram, escitalopram, fluoxetine, sertraline, and vortioxetine have been deemed more tolerable than other antidepressants, whereas amitriptyline, clomipramine, duloxetine, fluvoxamine, trazodone, and venlafaxine had the highest dropout rates[ 53 ] because of their more frequent and severe side effects. Nausea and vomiting were the most common reasons for treatment discontinuation; sexual dysfunction, sedation, priapism, and cardiotoxicity were also reported[ 31 , 41 ].

Ketamine and related molecules

In intravenous sub-anesthetic doses, ketamine has very quick effects on resistant unipolar (and, possibly, bipolar) depression and acute suicidal ideation[ 54 , 55 ]. The antidepressant effect of ketamine can persist for several days but eventually wanes. A few reports are have cited oral and intranasal formulations of ketamine for treatment-resistant depression[ 56 , 57 ], but there is still no data about the potential link between the onset of action and the route of administration.

Common adverse effects of ketamine include dizziness, neurotoxicity, cognitive dysfunction, blurred vision, psychosis, dissociation, urological dysfunction, restlessness, headache, nausea, vomiting, and cardiovascular symptoms[ 58 ]. Such adverse effects tend to be brief in acute, low-dose treatments[ 36 ], whereas prolonged exposure may predispose patients to neurotoxicity and drug dependence[ 56 ]. Lastly, since ketamine is associated with a higher risk of drug abuse and addiction, it cannot be recommended in daily clinical practice[ 59 , 60 ].

Ketamine is not a miracle drug, and many important factors still need to be defined, such as the most effective dose and the optimal administration route[ 61 , 62 ]. The current lack of guidelines about the therapeutic monitoring of ketamine treatment for depression further complicates the expanding use of this treatment[ 56 ]. Even though ketamine might never reach the market, it has stimulated research in the neurobiology of depression, including studies on potential fast and long-lasting antidepressants.

Ketamine has an active metabolite (hydroxynorketamine) that can produce rapid and sustained glutamatergic stimulation. It also seems to be free of many of the safety problems associated with ketamine and, thus, should be studied.

Research on the S-enantiomer of ketamine (S-ketamine, or esketamine, especially intranasal) could also be valuable, as it has a 3 to 4 times greater affinity than ketamine for the N-methyl-D-aspartate (NMDA) receptor[ 40 ]. It was approved by the United States Food and Drug Administration in March 2019 for treatment-resistant depression. However, current knowledge about the effects of prolonged esketamine therapy is still preliminary. In addition, regarding the potential risk of abuse, esketamine use must be carefully monitored[ 63 - 65 ].

Other glutamate receptor modulators have been evaluated in small studies as monotherapy agents or as adjuncts to other antidepressants. Examples include noncompetitive NMDA receptor antagonists (memantine, dextromethorphan/quinidi-ne, dextromethorphan/bupropion, and lanicemine), NR2B subunit-specific NMDA receptor antagonists (traxoprodil), NMDA receptor glycine site partial agonists (D-cycloserine, rapastinel), and metabotropic glutamate receptor antagonists (basimglurant, declogurant)[ 66 - 68 ] (Table ​ (Table1). 1 ).

Main classes of antidepressants with their date of approval, contributions, and disadvantages

NMDA: N-methyl-D-aspartate; SSRI: DSelective serotonin reuptake inhibitors; MDD: Major depressive disorder; MAOI: Monoamine oxidase inhibitor.

Perspectives

A purely neurotransmitter-based explanation for antidepressant drug action-especially serotonin-inhibiting drugs-is challenged by the significant percentage of patients who never achieve full remission[ 6 ] and the delayed clinical onset, which varies from two to four weeks. Moreover, studies show an acute increase in monoamines in the synaptic cleft immediately following treatment[ 69 ], even when the depletion of tryptophan (serotonin’s precursor) does not induce depressive-like behavior in healthy humans[ 70 , 71 ].

This finding shows that research on the pharmacological options for treating depression must go beyond monoaminergic neurotransmission systems. Research on the development of new antidepressants should explore several mechanisms of action on several types of receptors: Antagonism, inhibition of the reuptake of neurotransmitters, and modulators of glutamate receptors, as well as interactions with α-amino-3-acid receptors, hydroxy-5-methyl-4-isoxazolepropionic, brain-derived neurotrophic factor, tyrosine kinase B receptor (the mechanistic target of rapamycin), and glycogen synthase kinase-3[ 72 ].

Identifying the cellular targets of rapid-acting agents like ketamine could help practitioners develop more effective antidepressant molecules by revealing other receptors involved in gamma-aminobutyric acid regulation and glutamate transmission[ 73 ].

PSYCHOTHERAPY

Psychotherapeutic interventions are widely used to treat and prevent most psychiatric disorders. Such interventions are common in cases of depression, psychosocial difficulties, interpersonal problems, and intra-psychic conflicts. The specific psychotherapy approach chosen for any given case depends on the patient’s preference, as well as on the clinician’s background and availability[ 74 ] . Psychotherapy for patients with depression strengthens the therapeutic alliance and enables the patient to monitor their mood, improve their functioning, understand their symptoms better, and master the practical tools they need to cope with stressful events[ 75 ]. The following subsections briefly describe psychotherapeutic interventions that have been designed specifically for patients with depression.

Overview of psychotherapy in depression

Depression-focused psychotherapy is typically considered the initial treatment method for mild to moderate MDD. Based on significant clinical evidence, two specific psychotherapeutic methods are recommended: Cognitive-behavioral therapy (CBT) and interpersonal therapy (IPT). Supportive therapy (ST) and psychoeducational intervention (PEI) have also been recommended, those the evidence supporting these methods s not as strong. In more cases of severe depression, ST and PEI are used only to augment pharmacological treatments.

After remission, CBT, PEI, and mindfulness-based cognitive therapy (MBCT) are proposed to maintain and prevent depression. However, when psychotherapy has been effective during the initial phases of a depressive episode, it should be continued to maintain remission and prevent relapses while reducing the frequency of sessions[ 25 , 75 , 76 ].

Specific and intensive psychotherapeutic support is recommended for patients with chronic depression because of high rates of comorbidity with personality disorders, early trauma, and attachment deficits. The European Psychiatric Association recommends using the Cognitive Behavioral Analysis System of Psychotherapy (CBASP) for treating chronic depression and utilizing specific approaches suited to each patient’s preferences[ 77 ]. All these therapeutic options are summarized in Figure ​ Figure1 1 .

Overview of psychotherapy in different clinical situations of depression. MDD: Major depressive disorder; CBT: Cognitive-behavioral therapy; IPT: Interpersonal therapy; ST: Supportive therapy; PEI: Psycho-educational intervention; MBCT: Mindfulness based cognitive therapy; SIPS: Specific and intensive psychotherapeutic support; CBASP: Cognitive Behavioral Analysis System of Psychotherapy.

Structured psychotherapies

Cognitive and behavioral therapies: Based on robust evidence, CBT is one of the most well-documented and validated psychotherapeutic methods available. Interventional strategies are based on modifying dysfunctional behaviors and cognitions[ 77 ]. CBT targets depressed patients’ irrational beliefs and distorted cognitions that perpetuate depressive symptoms by challenging and reversing them[ 3 ]. Thus, CBT is a well-known effective treatment method for MDD[ 78 ] and has been recommended in most guidelines as a first-line treatment[ 79 - 81 ].

However, the effectiveness of CBT depends on patient’s capacity to observe and change their own beliefs and behaviors. Some simple techniques were developed to overcome this issue, especially in primary care management. Behavioral activation is one such technique, consisting of integrating pleasant activities into daily life to increase the number and intensity of the positive interactions that the patient has with their environment[ 82 , 83 ].

Acceptance and commitment therapy is another form of CBT. This type of therapy, which is based on functional contextualism, can help patients accept and adjusting to persistent problems. It appears to be effective in reducing depressive symptoms and preventing relapses[ 77 , 84 ].

Another form of CBT is computerized CBT (CCBT), implemented via a computer with a CD-ROM, DVD, or online CCBT, allowing patients to benefit from this therapy under conditions of reduced mobility, remoteness, confinement, or quarantine[ 79 ] .

CCBT and guided bibliotherapy based on CBT could be considered for self-motivated patients with mild to moderate major depression or as a complementary treatment to pharmacotherapy[ 25 ]. CBT is also recommended for patients with resistant depression in combination with antidepressants[ 85 ].

Schema therapy is another CBT-derived therapy that can be used in patients who have failed classical CBT, like patients with personality disorder comorbidity. Schema therapy is about as effective as CBT for treating depression[ 86 ]. In adolescent patients with depression, CBT is also a recommended option with plenty of evidence from multiple trials. Meanwhile, it remains the first-line treatment in children despite mixed findings across trials[ 87 ] . CBT is also a promising option for elderly depressed patients, though substantial evidence is still lacking because of the limited data on the subject[ 88 ] .

IPT: The goal of IPT is to identify the triggers of depressive symptoms or episodes. These triggers may include losses, social isolation, or difficulties in social interactions. The role of the intervention is to facilitate mourning (in the case of bereavement), help the patient recognize their own affect, and resolve social interaction dysfunction by building their social skills and social supports[ 89 ]. IPT, like CBT, is a first-line treatment for mild to moderate major depressive episodes in adults; it is also a well-established intervention for adolescents with depression[ 25 ] .

Problem-solving therapy: The problem-solving therapy (PST) approach combines cognitive and interpersonal elements, focusing on negative assessments of situations and problem-solving strategies. PST has been used in different clinical situations, like preventing depression among the elderly and treating patients with mild depressive symptoms, especially in primary care. Despite its small effect sizes, PST is comparable to other psychotherapeutic methods used to treat depression[ 88 , 90 ].

Marital and family therapy: Marital and family therapy (MFT) is effective in treating some aspects of depression. Family therapy has also been used to treat severe forms of depression associated with medications and hospitalization[ 91 ]. Marital and family problems can make people more vulnerable to depression, and MFT addresses these issues[ 92 ]. Marital therapy includes both members of the couple, as depression is considered in an interpersonal context in such cases. Some of the goals of this therapy are to facilitate communication and resolve different types of marital conflict. Family therapy uses similar principles as other forms of therapy while involving all family members and considering depression within the context of pathological family dynamics[ 93 ].

ST: Although ST is not as well-structured or well-evaluated as CBT or IPT, it is still commonly used to support depressed patients. In addition to sympathetic listening and expressing concern for the patient’s problems, ST requires emotionally attuned listening, empathic paraphrasing, explaining the nature of the patient’s suffering, and reassuring and encouraging them. These practices allow the patient to ventilate and accept their feelings, increase their self-esteem, and enhance their adaptive coping skills[ 94 ].

Psychodynamic therapy: Psychodynamic therapy encompasses a range of brief to long-term psychological interventions derived from psychoanalytic theories. This type of therapy focuses on intrapsychic conflicts related to shame, repressed impulses, problems in early childhood with one’s emotional caretakers that lead to low self-esteem and poor emotional self-regulation[ 93 , 95 ]. Psychodynamic therapy’s efficacy in the acute phase of MDD is well-established compared to other forms of psychotherapy.

Group therapy: The application of group therapy (GT) to MDD remains limited. Some data support the efficacy of specific types of GT inspired by CBT and IPT[ 96 - 98 ]. Group CBT for patients with subthreshold depression is an effective post-depressive-symptomatology treatment but not during the follow-up period[ 99 ]. Supportive GT and group CBT reduce depressive symptoms[ 96 ], especially in patients with common comorbid conditions[ 100 ]. However, studies are still lacking in this domain.

MBCT: MBCT is a relatively recent technique that combines elements of CBT with mindfulness-based stress reduction[ 101 ]. Studies have shown that eight weeks of MBCT treatment during remission reduces relapse. Thus, it is a potential alternative to reduce, or even stop, antidepressant treatment without increasing the risk of depressive recurrence, especially for patients at a high risk of relapse ( i.e. , patients with more than two previous episodes and patients who have experienced childhood abuse or trauma)[ 102 ].

Other psycho-interventions

Psycho-education: This type of intervention educates depressed patients and (with their permission) family members involved in the patient’s life about depression symptoms and management. This education should be provided in a language that the patient understands. Issues such as misperceptions about medication, treatment duration, the risk of relapse, and prodromes of depression should be addressed. Moreover, patients should be encouraged to maintain healthy lifestyles and enhance their social skills to prevent depression and boost their overall mental health. Many studies have highlighted the role of psycho-education in improving the clinical course, treatment adherence, and psychosocial functioning in patients with depression[ 103 ].

Physical exercise: Most guidelines for treating depression, including the National Institute for Health and Care Excellence, the American Psychiatric Association, and the Royal Australian and New Zealand College of Psychiatrists, recommend that depressed patients perform regular physical activity to alleviate symptoms and prevent relapses[ 104 ] . Exercise also promotes improvements in one’s quality of life in general[ 105 ] . However, exercise is considered an adjunct to other anti-depressive treatments[ 25 ] .

Although psychotherapy is effective for treating depression and improving patients’ quality of life, its direct actions against depressive symptoms are not fully understood[ 106 ]. Identifying factors ( e.g. , interpersonal variables) linked to treatment responses can help therapists choose the right therapeutic strategy for each patient and guide research to modify existing therapies and develop new ones[ 107 ].

Since depression is a primary care problematic, simplifying psychotherapy procedures will increase the use of psychological interventions for depression, especially in general practice. Brief forms (six to eight sessions) of CBT and PST have already shown their effectiveness for treating depression[ 108 ]. Nevertheless, simpler solutions must be made available to practitioners to help them manage and prevent depression.

SOMATIC TREATMENTS

In many situations, depression can also be managed via somatic treatments. ECT is the most well-known treatment for resistant depression, and solid evidence supports its effectiveness and safety. In recent decades, various innovative techniques have been proposed, such as repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), vagus nerve stimulation (VNS), deep brain stimulation (DBS), and magnetic seizure therapy, with varying efficiency levels[ 109 ].

ECT is arguably the most effective treatment modality in psychiatry, and its superiority over pharmacotherapy for major unipolar depression is widely supported[ 110 ]. ECT reduces the number of hospital readmissions and lightens the burden of depression, leading to a better quality of life[ 111 , 112 ].

Moreover, ECT is considered safe[ 113 ]. Advances in anesthesia and ECT techniques have decreased complications related to ECT while also improving cognitive outcomes and patient satisfaction.

However, the stigma surrounding ECT limits its use. Most misconceptions date back to early ECT techniques (when it was performed without muscle relaxants or anesthesia). Nevertheless, some people still consider ECT as the last option for treating depression, even though most studies indicate that ECT is more beneficial in patients with fewer pharmacological treatments[ 114 - 116 ].

ECT is typically recommended for patients with severe and psychotic depression, a high risk of suicide, or Parkinson’s disease, as well as pregnant patients[ 117 - 119 ]. The maintenance ECT also appears to prevent relapses[ 120 ]. The current practice of ECT continues to improve as protocols become more advanced, mainly owing to bioinformatics, and as more research is carried out in this domain[ 121 - 125 ].

This method, which is a type of biological stimulation that affects brain metabolism and neuronal electrical activity, has been widely used in research on depression[ 126 ]. Recent literature shows a significant difference between rTMS and fictitious stimulation regarding its improvements in depressive symptoms[ 127 ]. Preliminary research has revealed synergistic ( e.g. , rTMS/quetiapine) and antagonizing ( e.g. , rTMS/cannabinoid receptor (CB1) antagonist) interactions between neuro-modulation and pharmacotherapy[ 128 ]. Treatments combining rTMS and antidepressants are significantly more effective than placebo conditions, with mild side effects and good acceptability[ 129 ]. Although these results are encouraging, they remain inconsistent due to differences in rTMS treatment frequencies, parameters, and stimulation sites[ 129 ]. Therefore, clinical trials with large sample sizes are needed to specify which factors promote favorable therapeutic responses. Also, additional preclinical research should investigate the synergistic effects of other pharmacological molecules and guide integrated approaches (rTMS plus pharmacotherapy).

This technique delivers weak currents to the brain via electrodes placed on the scalp[ 130 ]. It is easy to use, safe, and tolerable[ 131 ]. The tDCS technique significantly outperforms the simulator in terms of the rate of response and remission[ 132 ]. However, its effect remains lower than that of antidepressants[ 133 ] and rTMS[ 134 ]. It can be used as a complementary intervention or as monotherapy to reduce depressive symptoms in unipolar or bipolar depression patients[ 135 ]. The antidepressant effects of tDCS may involve long-term neuroplastic changes that continue to occur even after the acute phase of treatment, which explains its delayed efficacy[ 135 ].

Recently, neurophysiological studies have shown that the clinical effects of tDCS do not have a direct linear relationship with the dose of stimulation[ 136 ]. tDCS, as a relatively simple and portable technology, is well-suited for remote supervised treatment and assessment at home, thus facilitating long treatment durations[ 136 ].

Since the optimal clinical effects of tDCS are delayed, future clinical trials should use longer evaluation periods and aim to identify responsive patients using algorithms[ 137 ].

VNS is a therapeutic method that has been used for the last sixteen years to treat resistant unilateral or bipolar depression. However, despite several clinical studies attesting to its favorable benefit-risk ratio and its approval by the Food Drug Administration in 2005, it is not used very often[ 138 ].

VNS involves the implantation of a pacemaker under the collarbone that is connected to an electrode surrounding the left vagus nerve. The left vagus nerve is preferred because it exposes the patient to fewer potential adverse cardiac effects. Indeed, most cardiac afferent fibers originate from the right vagus nerve[ 139 ]. Since the turn of the century, numerous studies have demonstrated the efficacy of VNS in resistant depression[ 140 - 142 ].

However, only one randomized, double-blind, controlled trial comparing VNS with usual medical treatment has been conducted over a short period of 10 wk[ 141 ]. Moreover, the results of this study did not indicate that the combination of VNS with typical medical treatments was better than the typical medical treatment on its own.

However, VNS has demonstrated progressively increasing improvements in depressive symptoms, with significant positive outcomes observed after six to 12 mo; these benefits can last for up to two years[ 143 ].

More long-term studies are needed to fully determine the predictors of the correct response.

According to the literature, DBS of the subgenual cingulate white matter (Brodmann area = BA 25) elicited a clinical response in 60% of resistant depression patients after six months and clinical remission in 35% of patients, with benefits maintained for over 12 mo[ 144 ]. The stimulation of other targets, in particular the nucleus accumbens, to treat resistant depression has gained interest recently. Behavioral effects indicate the quick and favorable impact of stimulation on anhedonia, with significant effects on mood appearing as early as week one after treatment begins[ 145 ].

Magnetic seizure therapy

Magnetic seizure therapy involves inducing a therapeutic seizure by applying magnetic stimulation to the brain while the patient is under anesthesia. This technique is still being investigated as a viable alternative to ECT to treat many psychiatric disorders. Evidence supporting its effectiveness on depressive symptoms continues to grow, and it appears to induce fewer neurocognitive effects than ECT[ 146 , 147 ].

Luxtherapy (phototherapy)

The first description of reduced depression symptoms due to intense light exposure was presented in 1984[ 148 ]. Optimal improvements were obtained with bright light exposure of 2500 Lux for two hours per day, with morning exposure shown to be superior to evening exposure[ 149 ].

A review and meta-analysis[ 150 ] showed that more intense (but shorter) exposures (10000 Lux for half an hour per day or 6000 Lux for 1.5 h per day) have the same efficacy. Importantly, this treatment method is effective both for those with seasonal and non-seasonal depression. Benefits of phototherapy related to sleep deprivation and drug treatments have also been reported[ 151 ].

Neuro-modulation treatments offer a range of treatment options for patients with depression. ECT remains the most documented and effective method in this category[ 151 ]. rTMS is an interesting technique as well, as it offers a well-tolerated profile[ 85 ], while tDCS offers encouraging but varying results that depend on the study’s design and the techniques used[ 130 ].

More investigations are needed to specify which indications are the best for each method according to the clinical and biological profiles of patients. The uses of such methods are expanding, probably, with their efficiency increasing when they are tailored to the patient. Furthermore, somatic interventions for depression need to be regularly assessed and integrated into psychiatrists’ therapeutic arsenals.

Treating depression is still a significant challenge. Finding the best option for each patient is the best way to obtaining short- and long-term effectiveness. The three principal methods available to caregivers are antidepressants, specifically structured psychotherapies, and somatic approaches. Research on depression pharmacotherapy continues to examine new molecules implicated in gamma-aminobutyric acid regulation and glutamate transmission. Also, efforts to personalize and simplify psychotherapeutic interventions are ongoing. Protocols using somatic interventions need to be studied in more depth, and their indications must be specified. ECT is the only somatic treatment with confirmed indications for certain forms of depression. Combinations of medications, psychotherapy, and somatic therapies remain the most effective ways to manage resistant forms of depression.

Conflict-of-interest statement: All authors declare that they have no conflict of interest related to this article.

Manuscript source: Invited manuscript

Peer-review started: March 31, 2021

First decision: June 5, 2021

Article in press: October 11, 2021

Specialty type: Medicine, research and experimental

Country/Territory of origin: Morocco

Peer-review report’s scientific quality classification

Grade A (Excellent): 0

Grade B (Very good): 0

Grade C (Good): 0

Grade D (Fair): D

Grade E (Poor): 0

P-Reviewer: Narumiya K S-Editor: Fan JR L-Editor: A P-Editor: Fan JR

Contributor Information

Rabie Karrouri, Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, Fez 30070, Morocco.

Zakaria Hammani, Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, Fez 30070, Morocco.

Roukaya Benjelloun, Department of Psychiatry, Faculty of Medicine, Mohammed VI University of Health Sciences, Casablanca 20000, Morocco.

Yassine Otheman, Department of Psychiatry, Moulay Ismaïl Military Hospital, Faculty of Medicine and Pharmacy, Sidi Mohamed Ben Abdellah University, Fez 30070, Morocco. [email protected] .

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Question: A student is writing a research paper on the links between diet and depression. Which of the following would be a good source for in-depth information that can be cited in the paper to support its argument? Select all that apply.Group of answer choicesThe Wikipedia entry on depression.The chapter on depression in her psychology textbook.An academic journal

An academic journal article on the impact of diet...

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