Systematic reviews do not adequately report or address missing outcome data in their analyses: a methodological survey

Abstract

Objectives: To describe how systematic review authors report and address categories of participants with potential missing outcome data of trial participants. Study Design and Setting: Methodological survey of systematic reviews reporting a group-level meta-analysis. Results: We included a random sample of 50 Cochrane and 50 non-Cochrane systematic reviews. Of these, 25 reported in their methods section a plan to consider at least one of the 10 categories of missing outcome data; 42 reported in their results, data for at least one category of missing data. The most reported category in the methods and results sections was ‘‘unexplained loss to follow-up’’ (n 5 34 in methods section and n 5 6 in the results section). Only 19 reported a method to handle missing data in their primary analyses, which was most often complete case analysis. Few reviews (n 5 9) reported in the methods section conducting sensitivity analysis to judge risk of bias associated with missing outcome data at the level of the meta-analysis; and only five of them presented the results of these analyses in the results section. Conclusion: Most systematic reviews do not explicitly report sufficient information on categories of trial participants with potential missing outcome data or address missing data in their primary analyses.