Longitudinal Mean Trends

Abstract

Our next task is to take the genetic simplex model as described in Chapter 14 and see whether the predicted change in variance over time is mirrored by a similar change in means. Although we said in the first chapter that inferences about means are not the primary focus of the study of individual differences, the longitudinal study is one in which changes in mean over time or growth, is of itself of considerable interest. This Chapter is not the first time that we have modeled information on means as well as covariances; in Chapter 8 we tested for the effects of sampling bias with the pairs concordant and discordant for study participation. Thus while at first glance the algebra and model formulation may seem a little intimidating, it covers what should by now be relatively familiar material.