Background: Inter-rater reliability (IRR) is mainly assessed based on only two reviewers of unknown expertise. The aim of this paper is to examine differences in the IRR of the Assessment of Multiple Systematic Reviews (AMSTAR) and R(evised)-AMSTAR depending on the pair of reviewers.

Methods: Five reviewers independently applied AMSTAR and R-AMSTAR to 16 systematic reviews (eight Cochrane reviews and eight non-Cochrane reviews) from the field of occupational health. Responses were dichotomized and reliability measures were calculated by applying Holsti's method (r) and Cohen's kappa (κ) to all potential pairs of reviewers. Given that five reviewers participated in the study, there were ten possible pairs of reviewers.

Results: Inter-rater reliability varied for AMSTAR between r = 0.82 and r = 0.98 (median r = 0.88) using Holsti’s method and κ = 0.41 and κ = 0.69 (median κ = 0.52) using Cohen's kappa and for R-AMSTAR between r = 0.77 and r = 0.89 (median r = 0.82) and κ = 0.32 and κ = 0.67 (median κ = 0.45) depending on the pair of reviewers. The same pair of reviewers yielded the highest IRR for both instruments. Pairwise Cohen's kappa reliability measures showed a moderate correlation between AMSTAR and R-AMSTAR (Spearman's ρ =0.50). The mean inter-rater reliability for AMSTAR was highest for item 1 (κ = 1.00) and item 5 (κ = 0.78), while lowest values were found for items 3, 8, 9 and 11, which showed only fair agreement.

Conclusions: Inter-rater reliability varies widely depending on the pair of reviewers. There may be some shortcomings associated with conducting reliability studies with only two reviewers. Further studies should include additional reviewers and should probably also take account of their level of expertise.

This article is published in the Journal "BMC Medical Research Methodology" 2017, 17:98.