There was no significant decrement in fit when the CPM was compared to the IPM (Δχ2=9.24, df=8, p=.32). Further, a lower AIC value was observed for the CPM, indicating that it provided a superior balance of fit and parsimony (IPM: AIC=88601.29, CPM: AIC=88592.79). Therefore, it appeared that in these data, the genetic and environmental influences on the ages of tobacco, alcohol, and cannabis initiation were mediated through a single latent factor. Full model estimates for the IPM are presented in Table S5 in supplemental materials.
