The parameter estimates and subsequent variance components obtained from fitting the covariate-adjusted multivariate model to the symptom count data (Figure 2, Table 4) confirm significant total genetic influences on HYP/IMP (a2 + d2 = 0.87), INATT (a2 + d2 = 0.82), and CDP (a2 = 0.29) after controlling for the effects of prenatal and childhood risk factors. Consistent with other reports of alcohol use in adolescence (Rhee et al., 2003; Rose et al., 2004), heritability for AlcProb was estimated at 13% and was non-significant. Shared environmental factors were important for CDP (c2 = .14) and even moreso for AlcProb (c2 = .34). Non-shared environmental factors, while small, were significant and accounted for between 14-18% of the total variance in HYP/IMP and INATT risk after controlling for prenatal and parental predictors. Larger non-shared environmental effects were found for CDP and AlcProb (e2=.57 and e2=.53, respectively). A significant contrast effect, in the form of sibling cooperation or maternal bias, was seen for HYP/IMP (s = .0737). Contrast effects for INATT were nonsignificant (s = -.0360).
