When Does Study Selection Need a PRISMA Flow Diagram?

Does Every Literature Review Need a PRISMA Flow Diagram?

You have probably seen the familiar boxes and arrows: thousands of records identified, duplicates removed, titles and abstracts screened, full texts assessed, exclusions recorded, and a much smaller number of studies finally included.

That is a PRISMA flow diagram, and it has become one of the most recognizable features of systematic review reporting.

Its familiarity can create a misconception, however. Researchers sometimes add a PRISMA diagram simply because their project contains a literature review, or because the diagram makes the methods look more systematic. Others conduct a genuinely systematic selection process but are unsure whether the diagram is necessary because they did not perform a meta-analysis.

The right question is not whether your paper contains a literature review. It is whether you conducted the kind of structured evidence-selection process that needs transparent reporting of how records moved from identification to final inclusion, and which reporting guideline applies to the review you actually performed.

Use a PRISMA Flow Diagram When Your Review Uses a PRISMA-Applicable Study-Selection Process

The Flow Diagram Reports What Happened to the Literature You Identified

PRISMA Is a Reporting Guideline for Systematic Reviews

PRISMA stands for Preferred Reporting Items for Systematic reviews and Meta-Analyses. PRISMA 2020 provides guidance for transparently reporting why a systematic review was conducted, what methods were used, and what the review found.

The flow diagram is one component of that reporting framework. The official PRISMA description states that it depicts the flow of information through the different phases of a systematic review, including the numbers of records identified, included, and excluded and the reasons for exclusions.

This distinction matters because PRISMA is primarily about reporting. It does not turn a review into a systematic review merely because the authors draw its flow diagram.

A PRISMA diagram should therefore represent a study-selection process that actually occurred. It should not be used as decoration or as a retrospective substitute for systematic methods.

You Do Not Need a Meta-Analysis to Use PRISMA

The word “meta-analyses” in PRISMA's name sometimes leads researchers to assume that the guideline applies only when statistical pooling is performed.

It does not.

PRISMA 2020 is a reporting guideline for systematic reviews, including reviews in which meta-analysis is not conducted. A systematic review may synthesize findings narratively, use other synthesis methods, or conclude that statistical pooling would be inappropriate because the included studies are too heterogeneous.

The need to report study selection does not disappear merely because no pooled effect size is calculated.

If your systematic review identifies records, screens them against eligibility criteria, retrieves potentially eligible reports, and determines a final included evidence base, a flow diagram remains useful for showing that process.

The Diagram Is About Selection, Not About Showing That You Used Several Databases

A PRISMA flow diagram is sometimes treated as a visual summary of database searching. Searching is only the beginning.

The diagram connects several stages of evidence selection:

PRISMA 2020 item 16a recommends describing the search and selection process from records identified through studies included, ideally using a flow diagram. The expanded checklist specifies the numbers that should be reported at the major stages of that process.

Records, Reports, and Studies Are Not the Same Thing

One of the most useful improvements in thinking about PRISMA flow is distinguishing three units that are often casually called “papers.”

This is why the numbers at different stages do not always form a simple one-paper-to-one-study sequence.

One study can generate several reports. Conversely, an article can occasionally describe more than one study. If you have already linked multiple papers originating from the same study or dataset, your flow reporting should preserve that distinction rather than counting each publication as an independent study.

Duplicate Records Belong Earlier in the Flow Than Duplicate Publications

Suppose Scopus and Web of Science both retrieve the same journal article. Those are duplicate records of the same report, and one can be removed before screening.

Now suppose two different journal articles later turn out to report the same trial. Those are not duplicate database records. They are multiple reports associated with the same underlying study.

The distinction affects how you count and report the review.

This is one reason duplicate publications need to be distinguished from ordinary search-result duplicates. A clean PRISMA flow depends on knowing what exactly was removed, screened, retrieved, and ultimately counted.

Reports Sought for Retrieval and Reports Assessed Are Different Numbers

PRISMA 2020 distinguishes reports sought for retrieval from reports actually retrieved and assessed for eligibility.

Imagine that 120 records survive title and abstract screening. You attempt to obtain all 120 full reports, but five cannot be retrieved despite reasonable efforts.

Your flow should not say that 120 full texts were assessed. Only 115 were available for that assessment.

This preserves an important methodological distinction. Failure to retrieve a report is not evidence that the underlying study failed your inclusion criteria.

Full-Text Exclusion Reasons Feed Into the Diagram

PRISMA 2020 asks reviewers to report primary reasons why retrieved reports did not meet the inclusion criteria. The flow diagram therefore depends on information collected during full-text screening.

Typical categories might include:

• ineligible population;
• ineligible intervention or phenomenon;
• ineligible study design;
• ineligible setting;
• ineligible publication type; or
• another prespecified eligibility criterion.

The categories should reflect the criteria of the particular review rather than a generic PRISMA vocabulary.

This is why tracking reasons for full-text exclusion while screening is much easier than attempting to reconstruct them when the manuscript is being written.

Not Every Excluded Title Needs Its Own Reason in the Diagram

The flow diagram reports the number of records excluded during initial screening. It does not require you to display a separate reason for every title and abstract that failed screening.

Detailed primary reasons become particularly important for reports excluded after retrieval and full-text eligibility assessment.

This distinction keeps the flow readable. If 4,000 records are excluded at title and abstract screening, a diagram listing 27 categories explaining all 4,000 decisions would rather defeat the purpose of a diagram.

PRISMA 2020 Provides Different Flow Diagram Templates

There is not just one universal PRISMA 2020 diagram.

The official PRISMA website provides separate templates depending on:

• whether the review is new or an update; and
• whether studies were identified only through databases and registers or also through other sources.

This produces four principal PRISMA 2020 templates:

Choose the template that reflects what you actually did. Do not force citation searching, website searching, reference-list checking, or other identification methods into database boxes merely to fit a simpler template.

Systematic Reviews Generally Should Report the Selection Flow

For a systematic review reported according to PRISMA 2020, the search and selection process should be reported from identification through final inclusion, ideally using a flow diagram.

In practice, many journals also explicitly require a PRISMA checklist and flow diagram for systematic review submissions. Journal instructions should therefore be checked in addition to the reporting guideline itself.

JBI's evidence-synthesis guidance likewise requires a complete account of study inclusion and states that a flowchart using the PRISMA template should be included for relevant JBI systematic reviews.

The diagram is particularly valuable because a systematic review makes claims based on a deliberately selected body of evidence. Readers need to understand how that body was produced.

Scoping Reviews Also Normally Report a Selection Flow

Scoping reviews have their own PRISMA extension: PRISMA-ScR. The extension includes reporting items for the selection of sources of evidence and the results of that selection process.

JBI's scoping review methodology incorporates PRISMA-ScR reporting guidance and expects transparent reporting of how sources were identified and selected.

So a scoping review is not an example of a review that should automatically omit a flow diagram simply because it is not a conventional intervention-effect systematic review.

The important principle is to use the reporting framework appropriate to the evidence synthesis you actually conducted.

A Narrative Literature Review Does Not Automatically Need PRISMA

A traditional narrative review may involve database searching, citation chasing, expert knowledge, iterative reading, and purposive selection of theoretical or empirical literature. That can be perfectly legitimate for the review's purpose.

But if the review did not use a systematic process in which a defined set of records moved through explicit eligibility stages, a PRISMA flow diagram may imply a level or type of selection procedure that did not occur.

For example, suppose you searched Google Scholar and several databases repeatedly while developing an argument, read papers recommended by colleagues, followed references when they appeared useful, and eventually cited 75 sources. Trying to reverse-engineer those activities into:

Records identified → records screened → full texts assessed → studies included

may produce numbers, but not necessarily a genuine PRISMA-compatible selection process.

A Thesis or Dissertation Does Not Automatically Require PRISMA Either

The academic format of the document does not determine whether PRISMA applies.

A thesis containing a systematic review may appropriately use PRISMA. A dissertation containing a scoping review may use PRISMA-ScR. A thesis with a conventional literature review chapter may not need either.

Your university, graduate school, adviser, ethics committee, or examination panel may impose additional formatting or methodological requirements. Those local requirements should be followed, but they should be distinguished from what PRISMA itself requires.

“This is for a thesis” is therefore not enough information to decide whether a PRISMA diagram belongs in the methods chapter.

A PRISMA Diagram Is Not Proof That the Search Was Comprehensive

A perfectly formatted diagram can accurately report a poor search.

Suppose the review searches one database with three poorly chosen keywords, retrieves 37 records, excludes 30, and includes seven studies. Those numbers can be placed neatly into a PRISMA flow diagram.

The diagram does not establish that relevant evidence was comprehensively identified.

Likewise, it does not prove that:

• the eligibility criteria were appropriate;
• screening was conducted correctly;
• duplicate publications were recognized;
• risk of bias was assessed adequately; or
• the synthesis was methodologically sound.

PRISMA improves reporting transparency. It should not be treated as a quality badge.

The Numbers Should Reconcile

A useful flow diagram is internally coherent.

If 1,000 records enter screening and 850 are excluded, the next stage should account for the remaining 150. If 150 reports are sought and five cannot be retrieved, 145 should remain available for assessment unless another explicitly reported event explains the difference.

If 145 reports are assessed and 100 are excluded, the remaining reports should reconcile with the number of included reports, remembering that the number of reports and number of studies may differ.

These checks sound elementary, but complicated search updates, multiple databases, automation, duplicate reports, and study-level linkage can make the arithmetic surprisingly easy to lose track of.

Do Not Invent Missing Numbers at the End

A PRISMA diagram depends on prospective record keeping.

If you did not track how many duplicates were removed, how many reports could not be retrieved, or why full texts were excluded, you may not be able to reconstruct those values reliably months later.

Do not estimate them merely to fill the boxes.

Instead, design your screening log from the beginning so that the necessary counts can be generated from actual records. Reference-management software, systematic review platforms, spreadsheets, or other tools can all support this if the stages and statuses are recorded consistently.

Automation Should Also Be Visible When Applicable

PRISMA 2020 explicitly provides for reporting the use of automation tools during study selection. Where applicable, the flow diagram can indicate how many records were excluded by humans and how many by automation.

This becomes increasingly relevant as machine-learning classifiers and AI-assisted screening systems are incorporated into evidence-synthesis workflows.

The presence of automation does not eliminate the need for transparent selection reporting. If anything, it increases the importance of making clear how records moved through the process and which decisions were made by humans, automated systems, or some combination of the two.

Use the Diagram Alongside Narrative Reporting

A flow diagram is compact, but it cannot explain every methodological detail.

Your methods should still describe:

• the eligibility criteria;
• how records and reports were screened;
• how many reviewers participated;
• whether they worked independently;
• how disagreements were resolved;
• how duplicate reports were handled; and
• any automation tools used.

The results section can then refer to the diagram when reporting how many records were identified, screened, excluded, retrieved, and included.

The diagram complements this explanation. It does not replace it.

From 2,400 Records to 38 Included Studies

Those figures can now populate the appropriate PRISMA flow template because they come directly from the screening records.

The final distinction between 43 reports and 38 studies is not a bookkeeping nuisance. It communicates that some underlying studies generated multiple publications, which is exactly why study-level tracking matters.

Common Misunderstandings About PRISMA Flow Diagrams

Choose the Flow Diagram From the Review You Actually Conducted

Before downloading a PRISMA template, identify your review type and the reporting guideline that applies to it.

Then verify that you possess the data required to populate the diagram. The easiest way to do this is not by counting backward from your included studies, but by maintaining accurate screening records from the beginning.

Before finalizing the figure, check that the counts reconcile and that your terminology distinguishes records, reports, and studies. If several researchers screened the literature, the accompanying methods should also explain how reviewers participated in study selection and how disagreements were resolved.

Before Adding a PRISMA Flow Diagram to Your Review

Questions About PRISMA Flow Diagrams

Use PRISMA to Report a Real Selection Process, Not to Create the Appearance of One

How to Cite This Guide

This guide is intended to be read, shared, and used in research, teaching, and academic work. If you draw on its ideas, explanations, or other content, please acknowledge the source by citing the guide. Doing so gives appropriate credit and helps your readers locate the original resource.