How to Conduct a Literature Review
A literature review is a critical and systematic examination of existing research and scholarly literature on a specific topic or research question. It involves searching, evaluating, and synthesizing a collection of published studies, articles, books, and other relevant sources to gain a comprehensive understanding of the topic's current state of knowledge.
Literature reviews are commonly conducted as a part of academic research projects, theses, dissertations, and scientific papers. They are essential for laying the groundwork for new research, establishing the significance of a study's research question, and showcasing the author's understanding of the existing literature in the field.
Engaging in the process of conducting a literature review cultivates critical thinking, research skills, and the ability to analyze and synthesize information. These skills are valuable to PAs for academic and professional growth.
I. Overview of Literature Reviews
a) Definition of a Literature Review
A literature review is a scholarly and systematic examination of existing academic and research literature on a particular topic.
It involves a thorough analysis and synthesis of published works, such as research articles, books, and other relevant sources, to identify and evaluate the key findings, methodologies, and trends in the field.
b) Purpose of Literature Reviews
The primary purpose of a literature review is to identify and analyze the key findings, methodologies, and trends within the existing body of research. By doing so, it helps to:
Identify Gaps in Knowledge: A literature review helps to identify areas where gaps in research exist, where further investigation is needed, or where inconsistencies in findings may arise.
Inform Research Design: Literature reviews provide a solid foundation for designing new research studies. By understanding what has already been studied, researchers can refine their research questions, select appropriate methodologies, and avoid duplicating previous efforts.
Support Evidence-Based Practice: Literature reviews contribute to evidence-based medicine and decision-making by presenting the most current and reliable information available on a particular topic.
Provide Context and Understanding: By synthesizing various studies, a literature review offers a broader context and understanding of the subject matter, helping researchers and practitioners to grasp the nuances and complexities involved.
Identify Conflicting Findings: A literature review may uncover conflicting or contradictory findings from different studies, helping researchers assess the overall strength of the evidence.
Analyze Trends and Patterns: Literature reviews help identify common themes, trends, and patterns within the literature. This analysis can shed light on emerging concepts or areas of consensus in a particular field.
Inform Policy and Practice: Policymakers can benefit from literature reviews, as they provide evidence-based insights to guide policy decisions and shape best practices in various domains, including healthcare, education, and public policy.
c) Types of Literature Reviews
There are several different types of literature reviews, each with distinct objectives and methodologies. The choice of the literature review type depends on the research question, the scope of the study, and the specific goals of the review.
Some common types of literature reviews include:
Narrative Literature Review: A narrative literature review is appropriate when researchers aim to provide a comprehensive overview of existing literature on a particular topic without following a strict systematic approach. It is commonly used as an introduction to a research paper or as background information in a thesis or dissertation. Researchers may choose a narrative review when time or resources are limited, and they seek to gain a broad understanding of the subject.
Pros: Quick and Informative They offer a comprehensive understanding of the current state of knowledge on a topic and help identify key themes and trends. Researchers have the freedom to select and present studies that align with their objectives, offering a more personalized perspective.
Cons: The selection of studies and synthesis of findings in narrative reviews may be subjective, leading to potential bias. Narrative reviews lack the rigor and transparency of systematic reviews, potentially compromising the credibility of the review's conclusions. They may not cover all available
evidence since they do not follow a predefined and comprehensive search strategy.
Systematic Literature Review: A systematic literature review is appropriate when researchers aim to provide a rigorous and evidence-based summary of all relevant research on a specific topic. It is ideal for answering focused research questions and informing evidence-based decision-making. Systematic reviews are commonly used when conducting literature reviews for research articles, clinical guidelines, or policy development.
Pros: Systematic reviews provide the highest level of evidence as they aim to minimize bias and maximize the reliability of findings. They help clinicians and policymakers make informed decisions based on the best available evidence. Systematic reviews follow a structured methodology, making the process transparent and reproducible.
Cons: Conducting a systematic review requires significant time, effort, and expertise in research methodology and statistical analysis. Systematic reviews may be limited by the availability and quality of existing research, especially for emerging or niche topics.
Meta-analysis: Meta-analyses are used as part of systematic reviews to quantitatively combine data from multiple studies when the research question involves assessing the overall effect size of an intervention or relationship. It is ideal for synthesizing data from similar studies with comparable outcomes.
Pros: Meta-analyses provide a more precise estimate of the effect size by pooling data from multiple studies. By combining data from multiple studies, meta-analyses increase statistical power and strengthen the validity of findings.
Cons: Meta-analyses rely on the availability of data with similar outcomes across studies, which may not always be feasible. Variability among studies, such as differences in study design or participant characteristics, can introduce challenges in conducting meta-analyses.
Scoping Review: Scoping reviews are suitable when researchers aim to map the breadth and depth of research literature on a broad or exploratory topic. They are used when the research question is open-ended and seeks to provide an overview of the available evidence.
Pros: Scoping reviews provide a broad understanding of the existing literature, identifying the range of studies available on the topic. Informative for Policy and Practice: They can inform policymakers and practitioners about the scope and diversity of research on a particular subject.
Cons: Scoping reviews do not typically assess the quality or risk of bias in included studies, as their primary goal is to map the literature. Due to their broad nature, scoping reviews may not delve deeply into specific research questions or provide definitive conclusions.
Integrative Literature Review: Integrative reviews synthesize both quantitative and qualitative research to gain a comprehensive understanding of a particular topic. They go beyond summarizing findings and attempt to uncover underlying concepts, patterns, and theories across different types of research.
Rapid Review: A rapid review is a streamlined version of a systematic review, designed to provide timely evidence in situations where traditional systematic reviews may take longer. Rapid reviews use accelerated search and appraisal methods, making them useful for informing urgent decision-making.
Umbrella Review: An umbrella review synthesizes findings from multiple systematic reviews and meta-analyses on related topics. It aims to provide a high-level summary and comparison of the results from multiple reviews.
II. Using PRISMA Guidelines for Systematic Reviews
Use the PRISMA framework to select studies
PRISMA stands for "Preferred Reporting Items for Systematic Reviews and Meta-Analyses." It is an evidence-based set of guidelines that provides a standardized framework for conducting and reporting systematic reviews and meta-analyses.
The PRISMA guidelines were developed to improve the transparency, quality, and comprehensibility of these types of literature reviews.
PRISMA guidelines are appropriate for any literature review that involves a systematic search, selection, and synthesis of studies to answer a specific research question or address a specific topic.
PRISMA Resources:
PRISMA 27 point checklist: PRISMA consists of a 27-item checklist that covers the key components of a systematic review or meta-analysis, including the title, abstract, introduction, methods, results, discussion, and funding sources.
PRISMA Flow Diagrams: This is a graphical representation that visually depicts the flow of information during the selection process of studies for inclusion in a systematic review or meta-analysis. It provides a clear and transparent overview of how researchers identify, screen, and include or exclude studies during the literature review process. The diagram helps readers understand the selection process and the reasons for the inclusion or exclusion of specific studies
III. How to Perform a Literature Review: Steps
Performing a literature review involves several essential steps to ensure a systematic and thorough examination of existing research on a specific topic.
If you opt not to use the PRISMA framework, we provided an overview of the steps to perform a literature review (we elaborate on each of the steps below this section):
Step 1: Define the Research Question: Start by clearly defining the research question or objective of your literature review. This will help focus your search and guide the entire process.
Step 2: Conduct a Literature Search: Use academic databases, libraries, and relevant search engines to find literature related to your research question. Employ keywords and controlled vocabulary terms to refine your search and retrieve relevant studies.
Step 3: Screen and Select Relevant Studies: Review the titles and abstracts of the retrieved studies to determine their relevance to your research question. Exclude studies that do not meet your criteria and select those that align with your objectives.
Step 4: Analyze and Synthesize Findings: Identify common themes, patterns, and trends across the selected studies. Analyze the evidence presented in the literature and synthesize the key findings.
Step 6: Draw Conclusions and Implications: Summarize the main findings of your literature review and draw conclusions based on the evidence presented in the studies. Discuss the implications of the findings for your research question and the broader field.
Step 7: Write the Literature Review: Organize your findings into a coherent narrative. Structure your literature review with clear headings and subheadings to guide the reader through the synthesis of information.
Step 1: Define your Research Question
a) Formulate your Research Questions
To formulate a research question for a literature review, begin by identifying a topic or area of interest that aligns with your research goals. Consider the scope and relevance of potential topics to your field of study.
Once you have selected a topic, narrow down the focus by evaluating its feasibility and the availability of literature and resources. Formulate a clear and concise research question that specifically addresses the objective you want to explore through the literature review.
Consider the purpose of the literature review, whether it's to provide an overview of the topic, identify gaps in the literature, or support a research proposal. Review existing literature on the topic to gain insights into the main findings, themes, and gaps, and use this information to refine and finalize your research question.
b) Clarify Inclusion and Exclusion Criteria
before you start your search, clearly define the criteria that will guide your selection process. These criteria should align with your research question and objectives.
Inclusion criteria should specify the characteristics that studies must possess to be considered relevant (e.g., study design, population, intervention, outcome measures).
Exclusion criteria should outline the characteristics that will cause studies to be excluded from your review (e.g., irrelevant topics, insufficient data).
Step 2: Conduct a Literature Search
a) Determine what type of Literature Search you will be performing
When determining the type of literature search to perform, carefully consider the specific goals of your research, the level of evidence required, and the available time and resources.
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Use a narrative literature review when your research question is exploratory and broad, and you want to provide a comprehensive overview of existing literature on a topic.
This type of literature review is suitable for introductory sections of research papers, background information in theses or dissertations, or when time and resources are limited.
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Choose a systematic literature review when your research question is specific and focused, and you aim to provide a rigorous and evidence-based summary of all relevant research on the topic.
Systematic reviews are ideal for answering well-defined research questions, informing evidence-based practice, and guiding clinical decision-making.
Consider conducting a systematic review when you have the resources and expertise to perform a comprehensive and methodical search and analysis of the literature.
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If your research question involves combining and analyzing quantitative data from multiple studies to estimate the overall effect size of an intervention or relationship, consider conducting a meta-analysis.
Meta-analyses are suitable when there is a sufficient number of studies with similar outcomes and methodologies.
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Opt for a scoping review when your research question is broad and you want to map the breadth and depth of the literature on a topic.
Scoping reviews are helpful when exploring emerging or complex subjects, identifying key concepts and themes, and providing an overview of available evidence.
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Choose an integrative review when your research question requires synthesizing findings from both quantitative and qualitative studies to gain a holistic understanding of a topic.
Integrative reviews are suitable for exploring the interrelationships between various aspects of a research question.
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Consider a rapid review when your research question requires timely evidence for urgent decision-making or policy development.
Rapid reviews use accelerated search and appraisal methods to provide quick and timely information.
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Opt for an umbrella review when your research question involves synthesizing findings from multiple systematic reviews and meta-analyses on related topics.
Umbrella reviews offer a broad perspective on the available evidence from different reviews.
b) Formulate your Search Terms
Based on your research question, develop a list of keywords and phrases that best represent the key concepts of your topic. Consider synonyms, related terms, and variations to ensure a comprehensive search
Utilize controlled vocabulary terms (e.g., MeSH terms in PubMed) that are specific to the databases you are using. Controlled terms help standardize the search and improve precision.
Refining your Search Strategy by using Boolean operators, quotation marks, truncation, filters, and brackets to refine your search.
c) Run & Review the Literature Search
Enter the formulated search strings into the chosen databases and search engines. Execute the search to retrieve relevant studies related to your research question.
Review the titles and abstracts of the retrieved studies to assess their relevance to your research question.
Be prepared to refine and modify your search strategy based on the initial results to ensure you capture all relevant literature.
Step 3: Screen and Select Relevant Studies
a) Review Titles and Abstracts
Start by reviewing the titles and abstracts of the retrieved studies.
Focus on the relevancy of each study to your research question based on the information presented in the titles and abstracts.
b) Apply Inclusion and Exclusion Criteria
Apply your predefined inclusion and exclusion criteria that you outlined in step 1 to the titles and abstracts of the studies that came up in your search.
Exclude studies that clearly do not meet your criteria to narrow down the list of potential articles.
c) Retrieve and Read Full Texts
For studies that seem relevant based on the titles and abstracts, obtain the full texts to further assess their suitability for inclusion. You can use academic databases, institutional subscriptions, or interlibrary loan services to access the full texts.
Thoroughly read the full texts of the selected studies to determine if they meet your inclusion criteria and align with your research question.
Evaluate the Quality of the Studies: Pay attention to study design, methodology, sample characteristics, data collection, and results.
d) Keep track of your Selections
Keep a record of the studies you have screened and selected, including the reasons for inclusion or exclusion.
Use reference management software or a spreadsheet to organize this information efficiently.
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Organizing and managing references is essential to maintaining a structured and efficient literature review process. Here are some tips on how to effectively organize and manage references using reference management software:
Choose a Reference Management Software:
Select a reference management software that suits your needs and preferences. Popular options include EndNote, Mendeley, Zotero, and RefWorks.
Consider factors such as user interface, compatibility with your operating system, and the ability to sync across devices.
Import References:
After retrieving the full texts of the selected studies, import the bibliographic information into your reference management software.
Most reference management tools allow you to import references automatically from academic databases or PDF files.
Organize References into Categories or Folders:
Create folders or categories within the software to organize your references systematically. You can categorize them based on themes, study types, or any other relevant criteria.
This organization will help you quickly locate specific references during the literature review process.
Add Keywords and Tags:
Utilize keywords and tags to annotate your references. These can be useful for searching and filtering references based on specific criteria.
Consider using standardized keywords related to your research topic for consistency.
Annotate References:
Add notes or annotations to the references, summarizing the key findings, methodologies, and other relevant information from each study.
These annotations will be helpful during the synthesis and writing stages of your literature review.
Track Review Status:
Use your reference management software to indicate the review status of each reference, such as "to be read," "reviewed," or "included."
This feature will help you keep track of your progress and ensure that no references are missed.
Cite While You Write:
Many reference management tools offer plugins that integrate with word processing software, allowing you to insert citations and create bibliographies seamlessly.
As you write your literature review, use these citation plugins to insert in-text citations and generate your reference list automatically.
e) Document Reasons for Exclusion
Document the reasons for excluding studies to maintain transparency and facilitate reporting in your final literature review.
Step 4: Analyze and Synthesize Findings
By carefully analyzing and synthesizing the findings of the selected studies, you will create a coherent and evidence-based narrative that addresses your research question.
Review Selected Studies:
Revisit the full texts of the selected studies, paying close attention to their methodologies, key findings, and results.
Take notes on the main points and relevant details from each study to have a comprehensive understanding of the literature.
Example: Read the full texts of ten selected studies that investigated the relationship between exercise and mental health in adults. Note down key information, such as the study design, participant characteristics, exercise interventions, and mental health outcomes.
Identify Common Themes and Patterns:
Look for common themes, concepts, or patterns that emerge from the findings of the selected studies.
Identify similarities and differences in the results across studies, considering factors such as study design, sample characteristics, and data analysis.
Example: Notice that most studies reported positive effects of exercise on mental health outcomes, such as reduced anxiety and depression. Identify a common theme across the studies that exercise is associated with improved mental well-being in adults.
Summarize Key Findings:
Summarize the key findings from each study, highlighting the main outcomes and results related to your research question.
Categorize the findings based on themes or subtopics to facilitate the synthesis process.
Example:
Summary of Study 1: A randomized controlled trial (RCT) found that regular aerobic exercise significantly reduced symptoms of depression in participants.
Summary of Study 2: A cross-sectional study demonstrated a positive correlation between exercise frequency and self-reported mental well-being.
Conduct a Thematic Analysis:
Perform a thematic analysis of the literature to identify recurring themes or concepts in the studies. This process involves coding the data from each study into relevant themes.
Use your notes and annotations to identify key themes and sub-themes that contribute to answering your research question.
Example: Code the data from each study to identify themes related to the effects of exercise on different aspects of mental health (e.g., anxiety, depression, stress).
Compare and Contrast Studies:
Compare the results of different studies to assess the consistency or variations in the findings.
Analyze any contradictions or conflicting evidence presented in the literature.
Example:
Compare Study 3 (RCT) and Study 4 (observational study): Both studies reported positive effects, but the RCT provided stronger evidence due to its controlled design.
Contrast Study 5 (longitudinal study) and Study 6 (meta-analysis): Both studies supported the exercise-mental health link, but the meta-analysis offered a more comprehensive view.
Address Gaps and Limitations:
Identify gaps in the literature, areas where research is lacking or incomplete.
Discuss any limitations of the studies that might affect the generalizability or validity of their findings.
Example:
Identify a gap: There are limited studies focusing on the effects of specific exercise types (e.g., yoga or strength training) on mental health outcomes.
Limitation: Some studies relied on self-reported measures of mental health, which may be subject to bias.
Synthesize the Evidence:
Synthesize the key findings from the selected studies to provide a cohesive and comprehensive narrative.
Analyze how the evidence contributes to answering your research question and how it aligns with existing knowledge in the field.
Example: Synthesize the key findings into themes: "Aerobic exercise is consistently associated with improved mood and reduced symptoms of depression." Discuss the overall evidence and suggest that exercise appears to have a positive impact on mental health in adults.
Present the Synthesis:
Organize your synthesis by themes, concepts, or relevant subtopics. Use clear and logical headings and subheadings to structure your presentation.
Provide an overview of each theme or sub-topic, summarizing the evidence from the studies.
Example: Themes Identified: "Effects of Exercise on Mood" and "Effects of Exercise on Symptoms of Depression." Under each theme, then present a summary of the studies and their findings related to that aspect of mental health.
Interpret the Findings:
Offer an interpretation of the findings, discussing the implications of the results in the context of your research question and objectives.
Address any discrepancies or contradictions in the literature and propose possible explanations.
Example: Interpret the evidence, highlighting the potential mechanisms through which exercise may improve mental health, such as the release of endorphins and stress reduction. Discuss the implications of these findings for public health and clinical interventions.
Use Visual Aids:
Consider using tables, charts, or diagrams to present the synthesized data visually, making complex information more accessible to the reader.
Visual aids can help demonstrate relationships between different studies and reinforce key points.
Example:
Create a table summarizing the key studies and their main findings related to different mental health outcomes.
Design a chart to illustrate the trend of exercise's effects on mental health outcomes over time.
Step 5: Draw Conclusions and Implications
By thoughtfully drawing conclusions and discussing the implications of your literature review, you contribute to the broader understanding of your research question.
Your conclusions and implications should leave the reader with a clear understanding of the impact and relevance of your findings.
Summarize Main Findings:
Provide a concise summary of the key findings from your literature review. This summary should highlight the main outcomes and patterns identified across the selected studies.
Use clear and straightforward language to communicate the major themes and subtopics that emerged from your analysis.
Draw Conclusions:
Based on the evidence presented in the literature review, draw conclusions about the research question or objective you initially posed.
Consider how the collective findings contribute to answering the research question and whether they support or challenge existing theories or knowledge.
Evaluate the Strength of Evidence:
Assess the strength of the evidence presented in your literature review. Reflect on the quality and credibility of the studies you included and how it impacts the certainty of your conclusions.
Acknowledge any limitations or gaps in the evidence and discuss their potential impact on the strength of your conclusions.
Discuss Implications:
Explore the implications of the findings for your research question and their broader significance for the field of study.
Discuss how the evidence presented may inform clinical practice, policy-making, or future research directions.
Address Inconsistencies or Contradictions:
If your literature review revealed inconsistencies or contradictions in the findings, address them in your discussion of implications.
Provide possible explanations for discrepancies and consider how they might influence the interpretation of the evidence.
Consider Practical Applications:
Discuss practical applications of the findings from your literature review. Consider how the results may guide decision-making, interventions, or educational practices in relevant fields.
Propose Future Research:
Identify areas that require further investigation based on the gaps or limitations identified in the literature review.
Suggest specific research questions or areas for future studies that could build upon the existing evidence.
Provide Recommendations:
Offer recommendations for practitioners, policymakers, or stakeholders based on the implications of your findings.
Consider how the evidence can be translated into practical actions or policies.
Present a Balanced Perspective:
Maintain objectivity and balance in your conclusions and implications. Acknowledge both the strengths and limitations of the evidence presented.
Avoid overgeneralization and ensure that your conclusions are grounded in the available evidence.
Step 6: Write your Literature Review
Here’s an outline of a Literature Review:
Introduction:
Introduce the topic of your literature review and provide context for your research question.
Clearly state the purpose and objectives of your literature review.
Overview of Research Question:
Briefly restate your research question and explain its significance in the context of existing literature.
Describe the scope and criteria used to select the studies included in your review.
Themes and Subtopics:
Present the main themes and subtopics that emerged from your analysis and synthesis of the literature.
Use clear headings and subheadings to organize the review and guide the reader through the content.
Synthesis of Findings:
Discuss the key findings from each selected study, summarizing their main outcomes related to the themes and subtopics.
Highlight similarities, differences, and patterns in the evidence across the studies.
Interpretation and Discussion:
Provide an interpretation of the collective evidence presented in the literature review.
Discuss the implications of the findings and how they contribute to the understanding of the research question.
Addressing Gaps and Limitations:
Acknowledge any gaps in the literature and limitations of the studies included in your review.
Suggest areas for future research and potential strategies to address identified limitations.
Conclusion:
Summarize the main findings and conclusions drawn from the literature review.
Emphasize the key contributions of your review to the existing knowledge in the field.
Recommendations (if applicable):
Provide recommendations for practitioners, policymakers, or future researchers based on the findings of your literature review.
Discuss the practical implications of the evidence presented.
Citations and References:
Ensure proper citation of all the studies and sources included in your literature review.
Follow the appropriate citation style (e.g., APA, MLA) for consistency.
Final notes
Learning to perform literature reviews is an invaluable skills for PAs.
References
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Muka, T., Glisic, M., Milic, J., Verhoog, S., Bohlius, J., Bramer, W., Chowdhury, R., & Franco, O. H. (2020). A 24-step guide on how to design, conduct, and successfully publish a systematic review and meta-analysis in medical research. European journal of epidemiology, 35(1), 49–60. https://doi.org/10.1007/s10654-019-00576-5
National Institutes of Health. (2019). PubMed: National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/
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Rethlefsen, M. L. et al (2021). PRISMA-S: an extension to the PRISMA Statement for Reporting Literature Searches in Systematic Reviews. Systematic reviews, 10(1), 39. https://doi.org/10.1186/s13643-020-01542-z
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