Within the CPM, we attempted to equate the paths from the latent factor to the ages of tobacco, alcohol, and cannabis initiation across men and women. The paths to alcohol and cannabis could not be equated (alcohol: Δχ2=8.35, df=1, p=.004; cannabis: Δχ2=17.73, df=1, p<.0001). Alcohol was more strongly related to the latent factor among men (standardized loading=.64, 95% CI [.56, .71]) than women (.50 [.43, .56]), and cannabis was more strongly related among women (.62 [.55, .69]) than men (.46 [.40, .52]). Given this information – as well as the evidence for some sex-specific effects in the univariate models – subsequent multivariate model-fitting was conducted separately among males and females. Table 4a displays the model-fitting results. For the men, the best-fitting model (I) was a full model. Although genetic and shared environmental influences could be dropped individually at the common and specific levels, dropping them simultaneously resulted in a significant decrement in fit. For the women, the best-fitting model (IV) contained common sources of shared environmental and unique environmental influence, as well as specific genetic and unique environmental factors. Table
