Umbrella Review

An umbrella review — also called an overview of reviews or review of reviews — sits one level above a systematic review or meta-analysis in the evidence-synthesis hierarchy. Instead of searching for and appraising primary studies, its unit of analysis is other systematic reviews and meta-analyses: it identifies every eligible review on a broader topic, appraises each review’s methodological quality, and synthesizes what they collectively show, typically across several related interventions, populations, or outcomes rather than a single narrow comparison. The term and its formal methodology were developed by the Joanna Briggs Institute (JBI), whose methodology working group published the foundational conduct-and-reporting guidance for the approach.

How an umbrella review differs from a systematic review or meta-analysis

The distinction is about what counts as the “study” being synthesized:

• Systematic review — systematically identifies and synthesizes primary studies (trials, cohort studies, etc.) on one focused question.
• Meta-analysis — the optional statistical step, usually nested inside a systematic review, that pools primary-study effect estimates into one quantitative summary.
• Umbrella review — identifies and synthesizes systematic reviews and meta-analyses themselves, comparing and contrasting their conclusions across a broader topic (for example, every intervention that has been systematically reviewed for a given condition, rather than one intervention at a time).

Because it works one layer removed from the primary literature, an umbrella review does not re-extract or re-analyze individual trial data the way a meta-analysis does. Most umbrella reviews synthesize findings narratively and in structured tables comparing review-level effect estimates and quality ratings; some go further and re-compute or compare pooled estimates across the included reviews, but that second-order statistical step is not what defines the design — the defining feature is the review-of-reviews scope. See systematic review vs. meta-analysis for how those two relate to each other before adding this third, broader tier on top.

Conduct: appraisal and overlap

Two methodological steps are specific to umbrella reviews and don’t have a direct equivalent one tier down:

• AMSTAR-2 appraisal. Because the “studies” being included are themselves reviews, umbrella reviews commonly use AMSTAR-2 (A MeaSurement Tool to Assess systematic Reviews, 2nd edition) to rate the methodological quality/confidence of each included systematic review, rather than the risk-of-bias tools (e.g., Cochrane RoB 2, ROBINS-I) used to appraise individual primary studies.
• Overlap of primary studies across included reviews. Because the same trial can be picked up by several different systematic reviews on related questions, umbrella reviews assess how much their included reviews overlap in the primary studies underlying them — commonly using the Corrected Covered Area (CCA) metric — so that double-counted evidence doesn’t inflate the apparent weight of a finding.

Reporting: PRISMA 2020 and the PRIOR statement

PRISMA 2020 is used to report the umbrella review itself — its own search, selection, and results — not to appraise the quality of the included reviews (that is AMSTAR-2’s job, above). Because PRISMA 2020 was written primarily with primary-study systematic reviews in mind, a purpose-built reporting guideline for this specific design also exists: the PRIOR statement (Preferred Reporting Items for Overviews of Reviews), published in 2022 specifically for overviews of reviews of healthcare interventions. PRIOR is PRISMA-adjacent in spirit and development lineage — produced by overlapping EQUATOR Network methodologists — but is its own distinct checklist rather than a numbered PRISMA extension, covering items such as clearly identifying the report as an overview of reviews in the title, and detailing how overlapping primary studies across included reviews were handled. Authors should also check whether the umbrella review’s protocol was prospectively registered, e.g. on PROSPERO, the same way a systematic review protocol would be.

Related designs it’s sometimes confused with

An umbrella review is not the same as a scoping review (which maps the extent of primary literature without appraising quality) or a network meta-analysis (which statistically compares multiple interventions using a shared network of primary-study evidence, still one tier below an umbrella review). See literature review vs. systematic review vs. scoping review and PRISMA and systematic review methodology for the broader landscape these designs sit within.

References

• Aromataris E, Fernandez R, Godfrey CM, Holly C, Khalil H, Tungpunkom P. “Summarizing systematic reviews: methodological development, conduct and reporting of an umbrella review approach.” International Journal of Evidence-Based Healthcare. 2015;13(3):132-140.
• Shea BJ, Reeves BC, Wells G, et al. “AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both.” BMJ. 2017;358:j4008.
• Pieper D, Antoine SL, Mathes T, Neugebauer EA, Eikermann M. “Systematic review finds overlapping reviews were not mentioned in every other overview.” Journal of Clinical Epidemiology. 2014;67(4):368-375 (Corrected Covered Area, CCA).
• Gates M, Gates A, Pieper D, et al. “Reporting guideline for overviews of reviews of healthcare interventions: development of the PRIOR statement.” BMJ. 2022;378:e070849.
• Page MJ, McKenzie JE, Bossuyt PM, et al. “The PRISMA 2020 statement: an updated guideline for reporting systematic reviews.” BMJ. 2021;372:n71.