class membership within the resulting GMM, probability of class membership was regressed on genotype. For these analyses, each of the SNPs were coded 0, 1, or 2, reflecting an additive genotypic model. This coding is in reference to the number of copies of the minor allele for all SNPs. These analyses were subsequently extended to the multivariate framework to test for moderation of genotypic effects by parental monitoring. All models in this study were fitted in Mplus version 5.0,46 allowing for single-stage modeling of classification into trajectories and testing of genetic/interaction effects. This method provides the advantage of using the probability of class membership as a continuous outcome variable rather than first classifying individuals into classes and using the resultant classes as discrete outcome variables in subsequent analyses, which results in a loss of information (and statistical power) that can systematically distort the characteristics of the latent classes.47 Odds ratios reflect pairwise comparisons of classification status (ie, the trajectories into which individuals are grouped on the basis of their highest probability of membership), but probability of class membership is the dependent variable modeled in analyses. Missing data are accommodated in Mplus via robust maximum likelihood estimation, which takes advantage of
