Clinical Trials

■■❚❙❘Chapter 29MultiplicityDorothea Nitsch, Duolao Wang,Tim Clayton, and Ameet BakhaiIn a clinical trial, information is often collected with multipleendpoints and baseline variables. In addition, outcomes areoften measured at several different time points. It is temptingto analyze this information by performing many statistical testssuch as comparisons of multiple endpoints, or undertakingmany separate subgroup analyses or comparisons of outcomemeasures at several time points during the course of the study.Consequently, the problem of ‘multiple testing’ or multiplicitycan occur where many statistical tests are performed, increasingthe probability of false-positive results (ie, the probability thatat least one result is significant at P < 0.05 by chance). In thischapter, we discuss the issue of multiplicity in the context ofclinical research, and highlight some strategies for dealingwith it.329