PRISMA flow diagram and reporting guideline

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) is the most widely used reporting guideline for systematic reviews and meta-analyses. The current version, PRISMA 2020, consists of a 27-item checklist and a flow diagram, and applies across research fields (not just health/medicine, where it originated).

The flow diagram

The flow diagram documents, stage by stage, how the initial pool of records became the final set of included studies — the same search-and-selection process described in Searching and selecting primary studies:

PRISMA flow diagram: identification of records from databases and other sources, screening with records excluded, eligibility assessment with full-text exclusions and reasons, and studies included in the review and in the meta-analysis

Identification: how many records were found (per database, plus other sources such as citation searching), and how many duplicates were removed before screening.
Screening: how many records were screened (title/abstract) and how many were excluded at this stage.
Eligibility: how many full texts were assessed, and how many were excluded — with the reason for each exclusion.
Included: how many studies were ultimately included in the review, and, of those, how many contributed data to the meta-analysis itself (the two numbers can differ, e.g. when a study is discussed narratively but doesn't report enough data for pooling).

Reporting exact counts at every stage is what lets readers judge how selective — and how reproducible — the search and selection process was.

Checklist and extensions

Beyond the flow diagram, the PRISMA checklist covers reporting items across the whole manuscript — title, abstract, methods, results, discussion, and funding/registration — not just the search process. Several extensions adapt the base checklist to specific designs, e.g. PRISMA-NMA for network meta-analysis and PRISMA-ScR for scoping reviews.

Where PRISMA fits

PRISMA is one of several reporting guidelines a meta-analysis can follow, alongside APA's MARS (Meta-Analysis Reporting Standards) and MOOSE (for meta-analyses of observational studies) — see Publishing a meta-analysis for how they relate.

The diagram above is redrawn, in this site's own style, from: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi: 10.1136/bmj.n71. Licensed under CC BY 4.0.