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Examining overlap of included studies in meta‐reviews: Guidance for using the corrected covered area index
Author(s) -
Hennessy Emily A.,
Johnson Blair T.
Publication year - 2020
Publication title -
research synthesis methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.376
H-Index - 35
eISSN - 1759-2887
pISSN - 1759-2879
DOI - 10.1002/jrsm.1390
Subject(s) - computer science , independence (probability theory) , meta analysis , systematic review , task (project management) , index (typography) , data science , data mining , medline , statistics , medicine , mathematics , political science , pathology , management , world wide web , law , economics
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.