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 official checklist, flow diagram templates, and supporting documents are maintained at prisma-statement.org.

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 searching and selecting process described in the meta-analysis steps:

PRISMA flow diagram: identification of records from databases and registers with removals before screening, screening with records excluded, retrieval of reports with reports not retrieved, eligibility assessment with reports excluded by reason, and studies included in the review with their reports

Identification: how many records were found (databases and registers), and how many were removed before screening — split into duplicates, records excluded by automation tools, and records removed for other reasons.
Screening: how many records were screened (title/abstract) and how many were excluded at this stage.
Retrieval: how many reports were sought for retrieval, and how many could not be retrieved.
Eligibility: how many reports were assessed for eligibility, and how many were excluded — with each exclusion reason reported and counted separately (reason 1, reason 2, etc.).
Included: how many studies were ultimately included in the review, and how many reports (publications) those studies correspond to — a single study can have multiple reports (e.g. a trial published across several papers), so the two counts can differ.

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.

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.