After fitting univariate and multivariate biometric models to the data for the age of first substance use, the same univariate and multivariate modeling procedures were applied to the ND, AUD, and CUD symptom counts. Subsequently, we fit a bivariate factor model (Figure 3). In this model, the first factor loads on the substance use initiation measures, and the second loads on the disorder measures. Consistent with the CPM, sources of genetic and environmental influence are modeled at the factor and residual levels. The relation between the two factors is modeled in terms of correlations in underlying additive genetic (rG), shared environmental (rC), and unique environmental (rE) influences. These correlations indicate the degree to which the genetic, shared environmental, and unique environmental influences on the age of substance use initiation are the same as the genetic, shared environmental, and unique environmental influences on substance use disorder.
