Understanding the PRISMA Flow Diagram: A Guide to Flow Diagrams in Literature Reviews

Introduction to the PRISMA Flow Diagram

What is a PRISMA Flow Diagram?

• PRISMA Flow Diagram is a key tool used in systematic reviews and meta-analyses.
• It is a visual representation that helps researchers track the process of selecting studies for inclusion in a systematic review.
• The diagram is part of the PRISMA Statement, which is designed to ensure transparency and completeness in reporting systematic reviews.
• It documents the number of records identified, the search results, the screening process, and the final selection of studies.
• The PRISMA Flow Diagram captures each stage of the systematic review, from the initial search through to the final inclusion of studies in the analysis.
• It is divided into several steps that provide a clear and concise overview of the inclusion/exclusion process.

Importance of Flow Diagrams in Systematic Reviews

• Clear Visualization: Flow diagrams are crucial for visualizing the progression of a systematic review. They provide a straightforward way to understand how many studies were included or excluded at each step of the process.
• Transparency: By documenting the search results and exclusion criteria, the PRISMA Flow Diagram promotes transparency. This ensures that the systematic review can be independently verified by others.
• Reproducibility: A detailed flow diagram helps others replicate the review. By showing exactly how studies were selected, it allows researchers to follow the same methodology, enhancing the credibility of the review.
• Standardization: The use of a standardized PRISMA diagram helps maintain consistency in reporting across different reviews. This is important when comparing results from different systematic reviews in a field.
• Reporting Systematic Reviews: Flow diagrams are essential for reporting systematic reviews and meta-analyses in line with the PRISMA Statement. They support accurate and comprehensive documentation of the review process, including search results and the number of records identified.
• Ensuring Completeness: The PRISMA Flow Diagram helps prevent selective reporting. By documenting all stages of the review, including the reasons for exclusions, it ensures that no important data is omitted.

Overview of PRISMA 2020 Flow Diagram

• PRISMA 2020 Statement and its PRISMA 2020 Flow Diagram bring updates and improvements to the previous versions, incorporating new research practices and terminology. It is particularly designed to ensure that systematic reviews reflect the current standards of reporting.
• The PRISMA 2020 Flow Diagram improves upon earlier versions by clarifying certain stages in the review process and enhancing how data are presented visually.
• The diagram is structured into different sections, each representing specific stages of the systematic review:
  • Identification: The number of records identified through database searches and other sources. This stage includes search results and any records added through other means (e.g., references from citation lists).
  • Screening: After records are identified, they undergo a screening process based on inclusion and exclusion criteria. This helps eliminate studies that don’t meet the standards for inclusion in your systematic review.
  • Eligibility: Studies that pass the screening phase are further assessed for eligibility. This step ensures that only studies which meet the specific criteria for your review are considered.
  • Included: The final step shows how many studies were included in the review. This is a crucial part of the reporting systematic reviews and meta-analyses, as it outlines the studies that were used in the final analysis.
• The PRISMA 2020 Flow Diagram for New Systematic Reviews is updated to include more detail about the process, and it can be adapted for use with meta-analyses as well.
• The diagram can be accessed and downloaded from the official PRISMA website, where PRISMA 2020 templates are available to help researchers incorporate the diagram into their reviews.
• Citation of the PRISMA 2020 Statement and the corresponding PRISMA Flow Chart is required to ensure that the systematic review is properly referenced.
• The diagram for new systematic reviews also includes spaces for reporting important metadata such as the number of records identified, the reasons for exclusions, and the final list of studies included.
• The PRISMA 2020 Flow Diagram reflects a more inclusive approach, accommodating a wider range of systematic review types and research methods.

Key Components of the PRISMA 2020 Flow Diagram

Stages in the PRISMA Flow Diagram

1. Identification of Studies:
   • Search Results: The first stage in the PRISMA 2020 Flow Diagram involves documenting the number of records identified during the initial search process.
   • Researchers search multiple databases and other sources like registers or citation managers to gather articles for review.
   • This stage is crucial in determining the initial pool of articles. Studies are identified based on the included searches of databases, registers, and other sources.
   • The left box of the PRISMA flow depicts the number of records retrieved, including those from trial registers and other sources.
   • Researchers should be cautious when importing records into a citation manager, ensuring no duplicate articles are included in the process.
   • This stage is the basis for later stages, as it reflects the search results in this box, showing how many articles were retrieved from each database.
2. Screening of Titles and Abstracts:
   • Title and Abstract Screening: After identifying studies, researchers review the titles and abstracts to determine whether articles meet the inclusion criteria.
   • The second box on your PRISMA shows the number of articles that move past the initial search to the screening phase.
   • Researchers screen the titles and abstracts of articles, marking those that are clearly irrelevant or do not meet the minimum eligibility requirements for further review.
   • The screening phase is important for narrowing down the articles for full-text review.
   • Reports sought for retrieval: If articles are unavailable or need further clarification, this step documents the efforts to obtain the full text of selected articles.
   • Preparation for full-text screening: Articles that pass this phase are set aside for more detailed examination in the next stage.
3. Eligibility Review of Full Texts:
   • Full-text Screening Stage for Eligibility: The third stage involves reviewing the full texts of the articles that passed the title and abstract screening.
   • The flow diagram depicts the flow of information as studies are assessed for their eligibility for inclusion in the review.
   • At this stage, researchers review the entire article to ensure that it meets the eligibility criteria for inclusion.
   • Excluded During the Eligibility Review: The diagram captures the number of records excluded during this phase. Exclusions could be based on methodological quality, relevance to the research question, or other predefined criteria.
   • Researchers must list their reasons for excluding certain articles, ensuring transparency in the review process. Common reasons for exclusion might include irrelevant study designs or inappropriate populations.
   • This phase plays a pivotal role in narrowing down the list of studies to those that are truly relevant to the systematic review.
4. Inclusion in the Systematic Review:
   • Final Inclusion: After all stages of screening and eligibility assessments, the final number of studies included in the systematic review is presented.
   • The four-phase flow diagram culminates here, showing the total number of articles reviewed and included in your systematic review.
   • This stage is critical for understanding the breadth of the review and ensures that the studies selected are based on rigorous criteria.
   • Articles that pass this final assessment are the basis for data extraction and synthesis in the review process.
   • The final selection is the last step of the PRISMA 2020 Flow Diagram and represents the studies that will contribute to the analysis and conclusions.

How the PRISMA Diagram Reflects the Systematic Review Process

• The PRISMA 2020 Flow Diagram provides a visual representation of the different phases of a systematic review.
  • Each phase of the review, from identifying studies to screening titles and full-texts, is clearly depicted, ensuring transparency and reproducibility.
  • The diagram allows readers to track the flow of information through the review process, making it easier to understand how studies were selected, excluded, and ultimately included.
  • By following the four-phase flow diagram, researchers can document and communicate their search methodology, improving the credibility and reliability of the review.
• Information Flow:
  • The PRISMA Flow Diagram captures key information at each step, ensuring that the systematic review can be easily followed.
  • From search results in the initial box to the eligibility review of full-texts, the diagram reflects how information moves through the review process, showing how each stage narrows down the number of studies.
• Ensuring Transparency and Reproducibility:
  • The flow diagram makes the systematic review process more transparent. By visually representing each phase of study selection, it enhances the basis for reporting systematic reviews.
  • If another researcher were to replicate the review, they could follow the documented flow to ensure that the same steps were taken. This is important for maintaining scientific rigor and credibility in the review process.
• Tracking Exclusions:
  • The flow diagram also tracks records excluded during the eligibility review, providing a clear justification for why certain studies were not included in the review.
  • This tracking is essential for understanding the review’s methodology and the reasons behind study exclusions. List your reasons for excluding articles in a transparent manner to provide a full picture of the selection process.

PRISMA 2020 Flow Diagram Templates

• The PRISMA 2020 Flow Diagram templates can be easily accessed and downloaded from the PRISMA website. These templates help standardize the process of reporting systematic reviews.
• Researchers can customize these templates based on their specific review needs, ensuring they follow the updated guidelines for preferred reporting items for systematic reviews.
• The template is structured to reflect the four-phase flow diagram, providing a simple yet effective way of documenting study selection and inclusion.
• By using the templates, researchers can ensure that their systematic review is in line with the latest PRISMA guidelines and is reported comprehensively and transparently.
• Customizing Templates for Different Reviews:
  • While the basic structure remains the same, the PRISMA 2020 Flow Diagram templates are flexible enough to be adapted for new systematic reviews, including reviews that included searches from a variety of sources (e.g., citation databases, trial registers).
  • The templates can also be tailored to review full-text articles, ensuring that only relevant studies are included in the systematic review.
  • Researchers can use the templates to document all necessary stages of their review, from the number of records identified to the final studies included, ensuring a complete and reproducible process.

The PRISMA 2020 Flow Diagram is an essential tool for conducting and reporting systematic reviews. By following the stages outlined in the diagram, researchers can ensure their review is comprehensive, transparent, and reproducible. The availability of customizable PRISMA templates ensures that the flow diagram is easy to implement and consistent with the latest standards in reporting systematic reviews.

How to Effectively Use the PRISMA Flow Diagram in Literature Reviews

Incorporating the PRISMA Flow Diagram in Your Systematic Review

• Start with Clear Objectives: Before beginning your systematic review, define the research question and eligibility criteria. This will guide your inclusion and exclusion decisions throughout the process.
• Use the PRISMA 2020 Flow Diagram Template: Download the latest PRISMA 2020 Flow Diagram templates from the PRISMA website. These templates help standardize your review process and ensure that you adhere to the most current reporting guidelines.
• Document Every Step: Ensure that every phase of the review, from study identification to inclusion, is documented in detail. This includes the number of records identified through search for each database individually, and the results of each search conducted.
• Track Studies in a Citation Manager: As you conduct the search, transfer the search results from each database to a citation manager. This ensures that you avoid reviewing duplicate articles and keeps your selection process organized.
• Screen Titles and Abstracts: The first step in narrowing down articles is screening titles and abstracts for articles. The PRISMA Flow Diagram helps you visualize the progression from the identification of studies to their screening for eligibility.
• Preparation for Full-Text Screening: Once articles pass the title and abstract screening, prepare them for full-text screening. At this stage, the PRISMA Flow Diagram will help you document the articles that move on for further review.
• Assess Eligibility for Inclusion: After full-text screening, assess whether the articles meet the eligibility criteria for inclusion in your systematic review. Clearly document all inclusions and exclusions in the PRISMA Flow Diagram to ensure transparency.

Best Practices for Using the PRISMA 2020 Flow Diagram

• Be Transparent and Comprehensive: The PRISMA Flow Diagram serves as a transparent record of your systematic review process. Ensure you document every decision, especially those leading to exclusions, such as reasons for rejecting studies during the eligibility review of full-texts.
• Accurate Categorization of Exclusions: For each article excluded during the eligibility review, be specific about the reasons for exclusion. Common reasons include not meeting the study design or population criteria. This is crucial for the basis for reporting systematic reviews and strengthens the credibility of your review.
• Include All Sources: Don’t rely solely on database searches. Include other sources like search trial registers, cited or citing references, and reports sought for retrieval to ensure your review is comprehensive and covers all relevant studies.
• Track Duplicates: As you move through the screening and eligibility assessment phases, be vigilant in avoiding reviewing duplicate articles. Duplicate records can skew your results and lead to overreporting.
• Keep a Record of Search Results: It’s vital to capture the search results from each database you search individually. This includes how many articles were retrieved from each source and where the studies were identified. This will help later if you need to replicate the search or address questions about the search methodology.
• Final Inclusion and Synthesis: The final phase of the PRISMA Flow Diagram shows how many articles were ultimately included in your systematic review. It’s important to document these clearly, as this is the core of your literature review.
• Use Consistent Terminology: When documenting each phase, use the PRISMA 2020 terminology consistently. Terms like “screening,” “eligibility,” and “inclusion” should be used clearly to avoid confusion during reporting.

Common Pitfalls to Avoid When Using PRISMA Flow Diagrams

1. Inadequate Search Documentation:
   • Pitfall: Failing to accurately document search results for each database search or other sources can undermine the transparency of your systematic review.
   • Solution: Always record the number of records identified from each source. Document the sources of the studies, such as trial registers or citation managers, and note how duplicates were managed.
2. Skipping the Screening Stages:
   • Pitfall: Some reviews may skip over essential steps like screening titles and abstracts or full-text review.
   • Solution: Ensure that every study goes through a clear and structured screening process. All exclusions and inclusions must be documented. The PRISMA Flow Diagram helps you visualize this entire progression.
3. Not Reviewing Full Texts Properly:
   • Pitfall: Moving studies to inclusion without a thorough review of full-text articles can introduce bias into your review.
   • Solution: Always conduct a careful review of the full text to assess eligibility for inclusion. Clearly document which studies meet the inclusion criteria, and provide reasons for those that do not.
4. Failure to Track Exclusions Properly:
   • Pitfall: Not keeping track of or documenting why studies were excluded can make your systematic review appear incomplete.
   • Solution: Use the PRISMA Flow Diagram to track the number of records excluded at each stage of the process. Ensure you list reasons for exclusions, which might include irrelevant study designs, population differences, or quality issues.
5. Overlooking Multiple Sources:
   • Pitfall: Relying too heavily on database searches without incorporating other sources like cited or citing references, search trial registers, or reports sought for retrieval can lead to missing valuable studies.
   • Solution: Be thorough in your search process. Expand your search to include a variety of sources to ensure your review is as comprehensive as possible. Use the PRISMA Flow Diagram to include all sources and avoid omitting key studies.
6. Inconsistent Use of Terminology:
   • Pitfall: Inconsistent or unclear use of terminology, such as referring to the same phase with different terms, can confuse the reader and detract from the credibility of the review.
   • Solution: Stick to the standardized terms recommended in the PRISMA 2020 Flow Diagram. This will make your review easier to understand and replicate by others in the research community.
7. Not Updating the Flow Diagram:
   • Pitfall: Failing to keep the PRISMA Flow Diagram updated during the review process can lead to errors and omissions in the final report.
   • Solution: Update the diagram regularly as you move through the different phases of the systematic review. Ensure that each stage reflects the most current status of your study selection.

By following best practices and avoiding these common pitfalls, you can effectively use the PRISMA Flow Diagram to guide your literature review. The diagram not only helps ensure that your review is systematic and reproducible, but it also enhances the transparency and credibility of your findings.