GENERAL LONGITUDINAL MODELING OF INDIVIDUAL-DIFFERENCES IN EXPERIMENTAL-DESIGNS - A LATENT VARIABLE FRAMEWORK FOR ANALYSIS AND POWER ESTIMATION

The generality of latent variable modeling of individual differences i n development over time is demonstrated with a particular emphasis on randomized intervention studies. First, a brief overview is given of b iostatistical and psychometric approaches to repeated measures analysi s. Second, the generality of the psychometric approach is indicated by some nonstaadard models. Third, a multiple-population analysis approa ch is proposed for the estimation of treatment effects. The approach c learly describes the treatment effect as development that differs from normative, control-group development. This framework allows for inter actions between treatment and initial status in their effects on devel opment. Finally, an approach for the estimation of power to detect tre atment effects in this framework is demonstrated. Illustrations of pow er calculations are carried out with artificial data, varying the samp le sizes, number of timepoints, and treatment effect sizes. Real data are used to illustrate analysis strategies and power calculations. Fur ther modeling extensions are discussed.