Addressing multiplicity issues of a composite endpoint and its components in clinical trials.

Randomized controlled clinical trials often use a composite endpoint as a primary endpoint especially when treatment effects or frequency of individual components of the composite are likely to be small and combining them makes clinical sense for the disease under study. An advantage of the composite endpoint is that, as it combines multiple endpoints to a single endpoint, it reduces or eliminates the multiplicity problem of testing multiple endpoints. In addition, accumulating evidence from individual endpoints into the composite endpoint can lead to better study power and reduce the study size and the duration of the trial. However, composite endpoints can also lead to ambiguous findings and consequently cause difficulty in interpreting study results, for example, when individual component endpoints of a composite show treatment effects in different directions. Also, multiplicity issues will arise if a study sponsor seeks efficacy claims for specific components of the composite or for a targeted subgroup of patients. This paper visits some of these issues and presents some solutions through applications of multiple testing strategies.