Association between switching of primary outcomes and reported trial findings among randomized drug trials from China

Background and Objective: To evaluate the association between the nature of findings and the switching of registered primary outcomes among randomized controlled trials (RCTs) from mainland China. Methods: This is a retrospective cohort study. We retrieved RCTs from trial registries and identified the corresponding journal articles from bibliographic databases until August 2019. Trial registries and journal articles were compared to evaluate whether registered primary outcomes with negative findings were more likely to be switched to secondary outcomes in the subsequent journal articles than those with positive findings. Results: Switching of registered primary outcomes occurred in 131 (45%) of 294 RCTs. A total of 450 registered primary outcomes were matched to 522 (37%) primary outcomes and 871 (63%) secondary outcomes in the journal articles. Among RCTs registered before they started, the odds of switching primary outcomes with negative findings were 2.64 (95% CI: 1.16–6.02) times the odds of switching those with positive findings. Among RCTs registered when they were ongoing, the odds of switching primary outcomes with negative findings were 8.84 (95% CI: 3.62–25.93) times the odds of switching those with positive findings. Conclusion: The nature of findings may play a role in how likely a prespecified primary outcome is switched subsequently.