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Examining overlap of included studies in meta‐reviews: Guidance for using the corrected covered area index
Open accessAbstract
Overlap in meta‐reviews results from the use of multiple identical primary studies in similar reviews. It is an important area for research synthesists because overlap indicates the degree to which reviews address the same or different literatures of primary research. Current guidelines to address overlap suggest that assessing and documenting the degree of overlap in primary studies, calculated via the corrected covered area (CCA) is a promising method. Yet, the CCA is a simple percentage of overlap and current guidelines do not detail ways that reviewers can use the CCA as a diagnostic tool while also comprehensively incorporating these findings into their conclusions. Furthermore, we maintain that meta‐review teams must address non‐independence via overlap more thoroughly than by simply estimating and reporting the CCA. Instead, we recommend and elaborate five steps to take when examining overlap, illustrating these steps through the use of an empirical example of primary study overlap in a recently conducted meta‐review. This work helps to show that overlap of primary studies included in a meta‐review is not necessarily a bias but often can be a benefit. We also highlight further areas of caution in this task and potential for the development of new tools to address non‐independence issues.
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“The Corrected Covered Area (CCA) method was used to assess overlap in the RCTs that were included across all eligible reviews.20”
From Effectiveness of exercise for improving cognition, memory and executive function: a systematic umbrella review and meta-meta-analysis (2025) · cites this paper as [20]
In the citing paper
“Since publication of the MOoR framework, methods for overlap have been published [17–19].”
From Managing overlap of primary study results across systematic reviews: practical considerations for authors of overviews of reviews (2021) · cites this paper as [17]
In the citing paper
“Our search strategy retrieved 119 unique records, and the forward citation searching retrieved 92 citations (Fig. 2). After deduplication 199 remained, and after screening abstracts and full text, seven were included [17–19, 28–31]. One additional conference citation was found through expert knowledge on the topic [32], and one paper recently published was included after completion of the first”
From Managing overlap of primary study results across systematic reviews: practical considerations for authors of overviews of reviews (2021) · cites this paper as [17]
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“First, CCA calculations for all primary studies across reviews, CCA calculations between 2 reviews only, and CCA calculations for one outcome [17] yield vastly different results.”
From Managing overlap of primary study results across systematic reviews: practical considerations for authors of overviews of reviews (2021) · cites this paper as [17]
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“The extent to which systematic reviews in a particular domain include the same studies varies widely, depending on many factors.(1,9) On the one hand, if reviews address similar questions with similar methods and integrate largely the same primary-level studies' Received: 26 July 2019 Revised: 22 October 2019 Accepted…”
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Metadata
- Authors
- Hennessy, E. A., & Johnson, B. T.
- Affiliations
- University of Connecticut (US)
- Corresponding author
- Hennessy, Emily A.
- Venue
- Research Synthesis Methods
- Publisher
- Wiley
- Published
- 2019-12-10
- Volume
- 11
- Issue
- 1
- Pages
- 134-145
- ISSN
- 1759-2879 (ISSN-L)
- 1759-2887
- PMC
- PMC8555740
- OpenAlex
- W2996727926
- Cited by
- 348
- References
- 36
- Citations by year
- 2026: 99 · 2025: 95 · 2024: 61 · 2023: 54 · 2022: 18 · 2021: 13 · 2020: 5 · 2019: 1
- FWCI
- 6.18
- Type
- journal article
- Language
- en
- Open access
- green
- europepmc.org
- Locations
- Research Synthesis Methods (publishedVersion)
- PubMed (publishedVersion)
- Europe PMC (PubMed Central) (acceptedVersion)
- PubMed Central (acceptedVersion)
- Funders
- National Institute on Aging (5U24AG052175)
- Topics
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Social Sciences › Library and Information Sciences › scientometrics and bibliometrics research
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Psychology Research and Bibliometrics
- Keywords
- meta-review, non-independence, evidence synthesis
- MeSH terms
- Abstracting and Indexing, Systematic Reviews as Topic, Algorithms, Blood Pressure, Decision Trees, Humans, Research Design, Meta-Analysis as Topic, Bias, Guidelines as Topic
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