to the covariance among dependence on different substances to SDV, especially in the case of alcohol in females. More specifically, the pattern of the cross-twin-cross-trait correlations and the univariate models (Table 4) indicated limited evidence for additive genetic effects on alcohol in females(h2 = 0%); however, in the multivariate model, which provides more power to estimate genetic and environmental effects, genetic effects emerged (h2 = 22%) as a result of being able to equate the phenotypic and etiological structures of SDV across males and females. Heritability estimates derived from the best-fitting CPM were 38%, 55%, and 19% for alcohol, tobacco, and cannabis in males, and 22%, 16%, and 43% for females, respectively.
