Table 4 presents the model fit statistics for the series of sex-limited univariate models of alcohol, tobacco, and cannabis dependence along with the parameter estimates of the best fitting of the three sex-limitation models. The full/base model (i.e., Model I) for each substance included A, C, and E influences that were estimated separately for each sex. Model I was compared to two reduced forms (i.e. Models II and III) by employing a Chi-Square difference test to determine the best fitting sex-limitation model. In all instances, model comparisons suggested no sex-specific additive genetic effects. Furthermore, for each substance, the Common Effects Sex-Limitation Model (Model II) provided a better fit to the data (based on the AIC statistic) compared to Model III, suggesting that the magnitude of genetic and environmental influences differed between males and females. Based on Model II, the heritability of alcohol, tobacco, and cannabis dependence symptom counts were 37%, 40% and 18% in males, and 0%, 43%, and 49% in females, respectively.
