Crossover experiments: A comparison of ANOVA tests and alternative analyses

Crossover experiments are really special types of repeated measures experim ents. The correct analysis of a repeated measures experiment depends on the structure of the variance-covariance matrix of the repeated measures, Cert ain structures of the variance-covariance matrix assure that analysis of va riance procedures lead to valid statistical tests. Other covariance structu res invalidate some of the analysis of variance tests. This paper provides conditions under which the traditional ANOVA tests are valid. For those sit uations when the traditional tests may be invalid, alternative test procedu res are proposed, and these procedures are compared to one another in a sim ulation study. These alternative procedures include degrees of freedom adju stment techniques, a multivariate model approach, and a mixed models (estim ated generalized least squares) approach. In cases where the usual ANOVA me thods are not valid, the multivariate model approach is the method that met the nominal size requirement for the hypotheses tests of equal treatment a nd equal carryover effects.