Heterogeneity of studies in anesthesiology systematic reviews: a meta-epidemiological review and proposal for evidence mapping.

Heterogeneity among the primary studies included in a systematic review (SR) is one of the most challenging considerations for systematic reviewers. Current practices in anaesthesiology SRs have not been evaluated, but traditional methods may not provide sufficient information to evaluate the true nature of these differences. We address these issues by examining the practices for evaluating heterogeneity in anesthesiology reviews. Also, we propose a mapping method for presenting heterogeneous aspects of the primary studies in SRs.We evaluated heterogeneity practices reported in SRs published in highly ranked anesthesiology journals and Cochrane reviews. Elements extracted from the SRs included heterogeneity tests, models used, analyses conducted, plots used, and I2 values. Additionally, we selected a SR to develop an evidence map in order to display clinical heterogeneity.Our statistical analysis showed 150/207 SRs reporting a test for statistical heterogeneity. Plots were used in 138 reviews to display heterogeneity. Subgroup analyses were the most commonly reported analysis (54%). Meta-regression and sensitivity analyses were used sparingly (25%; 23% respectively). A random effects model was most commonly reported (33%). Heterogeneity statistics across meta-analyses suggested that, in our sample, the majority (55%) did not present sufficient heterogeneity to be of great concern. Cochrane reviews (n=58) were also analysed. Plots were used in 88% of Cochrane reviews. Subgroup analysis was used in 59% Cochrane reviews, while sensitivity analysis was used in 62%.Many reviews did not provide sufficient detail regarding heterogeneity. We are calling for improvement to reporting practices.