The pattern of twin correlations (MZ vs. DZ) for the four outcomes of interest to this report are presented in Table 2. The correlations suggest that for INATT (rMZ = .79; rDZ = .29) and HYP/IMP (rMZ = .87; rDZ = .36) both additive and dominant genetic factors influence these outcomes and that shared environmental influences are not significant. However, for CDP (rMZ = .49; rDZ = .32) and AlcProb (rMZ = .58; rDZ = .50), it appears that additive genetic and shared environmental influences are important. These assumptions were confirmed by fitting univariate models that allowed for shared environmental influences (for INATT and HYP/IMP) or non-additive genetic effects (for CDP and AlcProb) to the symptom count measures. For INATT and HYP/IMP, shared environmental influences were estimated at zero (95% CI = 0.00-0.02 for INATT; 95% CI = 0.00-0.03 for HYP/IMP). For CDP and AlcProb, non-additive influences were estimated at zero (95% CI = 0.00-0.05 for CDP; 95% CI = 0.00-0.12 for AlcProb).
