Methodological review showed correct absolute effect size estimates for time-to-event outcomes in less than one-third of cancer-related systematic reviews

Abstract

ObjectivesTo evaluate in how many cancer-related Cochrane reviews hazard ratio (HR)-based absolute effects in summary of findings (SoF) tables have been correctly calculated and reported. Study Design and SettingWe identified all Cochrane cancer intervention reviews that reported an HR for at least one outcome and provided a SoF table, published between January 2011 and December 2017 in the Cochrane Database of Systematic Reviews. ResultsIn 28 reviews (29%) of 96 included Cochrane reviews, absolute effects in the SoF tables were calculated in a correct manner. In 23 reviews (24%), absolute effects had been correctly calculated, but there was no explanation given why authors calculated event-free survival (e.g., overall survival) throughout the review but reported number of events in SoF tables (e.g., death). Twelve reviews (13%) provided incorrect absolute effects. For seven reviews (7%), it was unclear if absolute effects were correctly calculated. In 26 (27%) reviews, no absolute effects based on the given HR were calculated. ConclusionsIn less than one-third of cancer-related Cochrane reviews, absolute effect size estimates were correctly calculated and reported. There is a need for guidance on how to calculate and report absolute effect estimates based on HR data.