Univariate model-fitting results are presented in Table S4 in supplemental materials and standardized full model estimates of A, C, and E for the full sample, men, and women are presented in Table 3. Inspection reveals that: (1) shared environmental influences explained a significant proportion of the variation in all substances; (2) genetic influences on the age of tobacco initiation were significant among women (.32 [.12, .53]), but not men (.19 [−.09, .47]); (3) genetic influences on the age of alcohol initiation were significant among men (.29 [.01, .58]), but not women (.21 [−.04, .45]); and (4) genetic influences on the age of cannabis initiation were not significant in men (.22 [−.07, .51]) or women (.18 [−.09, .45]).
