Dangers of including outcome at baseline as a covariate in latent change score models
Latent change score modelling is a version of structural equation modelling for measuring change between measurements. It seems quite common to regress change on the initial value included in the calculation of the change score (i.e. ΔY (= Y2 – Y1) is regressed on Y1). However, similarly as in simpler regression analyses, this procedure may make findings susceptible to the influence of regression to the mean. This suspicion was verified in the present simulations. An empirical application, including re-analyses of previously published data, indicated that previously claimed reciprocal promoting effects of vocabulary and matrix reasoning on each other’s longitudinal development may actually be due to regression to the mean. Researchers are recommended not to regress change on the initial value included in the calculation of the change score when employing latent change score modelling, or at least to verify findings with analyses omitting this parameter.