Composite outcomes in randomized controlled trials: Advantages and pitfalls

In medical studies, randomized controlled trials (RCTs) offer strong proof of the connection between a treatment and its effects on health. Typically, RCTs report a primary outcome along with additional secondary outcomes to evaluate the effectiveness of treatment. Generally, the primary outcome is the focus on determining cause and effect, whereas the secondary outcomes are used to generate hypotheses. To increase the study power, composite endpoints are sometimes used as the primary outcome, especially when the expected event rates are low. This article outlines the current practices in selection, analysis, presentation, and interpretation of composite outcomes in RCTs to determine treatment efficacy.