The analysis of repeated measures designs in medical research

Abstract

Medical researchers can employ repeated measures designs to study the effects of a treatment over time or when each subject receives all treatments. Univariate F tests and multiple comparison procedures for comparing means constitute the methods to test for the presence of treatment effects. For validity, however, these tests must satisfy the sphericity assumption. To circumvent the biasing effects of non-sphericity, this paper shows the applicability of the Greenhouse and Geisser three stage approach for univariate omnibus hypothesis testing in repeated measures designs containing any number of repeated factors. In addition, we present a multiple comparison procedure which provides a valid or robust test and thus controls the overall probability of a Type I error.