Satisfying a simplex structure is simpler than it should be: A latent curve analysis revisit

This article is concerned with the utility of the structural equation modeling (SEM) methodology for studying change. Two broad classes of models are considered, individual and group change models. The relationship between the constant rate of change and simplex models, as popular representatives of either class, is examined. Both models are shown to be special cases of the comprehensive latent curve analysis (Meredith & Tisak, 1990). Sensitivity of its models to differences in individual growth curves is demonstrated on data from Rogosa and Willett (1985a). Benefits of studying longitudinal change using SEM and related issues of model choice are discussed.