Authors should clearly report how they derived the overall rating when applying AMSTAR 2-a cross-sectional study.

Objectives: A measurement tool to assess systematic reviews (SRs) 2 (AMSTAR 2) allows for deriving the overall confidence in an SR. We investigated how authors derived the overall confidence rating and whether different schemes lead to different results.
Study Design and Setting: We compared three different schemes (original 7-item scheme, a self-developed 5-item scheme, and the AMSTAR Web site) to derive the overall confidence in AMSTAR 2 using two distinct samples of SRs. Multiple bibliographic databases were searched for articles to analyze how AMSTAR 2 was applied by others.
Results: In both samples (n = 60 and n = 58), the Friedman test revealed a significant difference between the schemes (P < 0.001). The Web site scheme was the least strict one, whereas between the 5-item and 7-item scheme, no differences were found in post hoc analyses. We included 53 publications applying AMSTAR 2 identified in our literature search. Only 37 of them (70%) used the original 7-item scheme. Less than half of them (18 of 37) reported how they derived the overall rating.
Conclusion: Authors should clearly report how they have derived the overall rating when applying AMSTAR 2. Reporting should allow for reproducing the overall ratings for editors, peer reviewers, and readers.
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