Reporting of Cochrane Systematic Review Protocols with Network Meta-Analyses--A Scoping Review

Publishing systematic review protocols is a fundamental part of systematic reviews to ensure transparency and reproducibility. In this scoping review, we aimed to evaluate reporting of Cochrane systematic review protocols with network meta-analyses (NMA). We searched all Cochrane NMA protocols published in 2018 and 2019, and assessed the characteristics and reporting of methodologies relevant to NMA. We reported frequencies for each reporting item. Forty-five protocols were assessed, including two for overviews and 43 for intervention reviews. Thirty-three (73%) were labelled as NMA protocols in the title. Forty-two (95%) justified the need of an NMA and 40 (89%) used appropriate search strategies to identify potential eligible studies. About half (24, 53%) considered the transitivity assumption when reporting inclusion criteria and 35 (78%) specified potential effect modifiers. Forty-three (96%) reported statistical software for NMA, 25 (56%) reported NMA model choice, 32 (71%) reported framework choice and 32 (71%) reported assumption about heterogeneity variances. Protocols varied in whether they reported methods for relative ranking (35, 78%), statistical inconsistency (40, 89%), reporting bias (44, 98%) and sources of heterogeneity (39, 87%). In conclusion, Cochrane NMA protocols reported multiple NMA-specific items well, but could be further improved, especially regarding transitivity assumptions. Our recommendations for NMA protocol reporting based on this scoping review could assist authors, reviewers, and editors to improve NMA protocols.