Parameter estimates from fitting the ACE biometric model separately to the five clinical phenotypes are given in Table 1. For each phenotype, the standardized estimate of the contribution of additive genetic factors (a2) is significant and large, with estimates for a2 ranging from .49 (for Alcohol Consumption) to .70 (for both Alcohol Dependence and Behavioral Disinhibition). The estimated contribution of shared environmental factors (c2) was moderate but significant for three of the phenotypes (ranging from .16 to .24) and zero or near-zero for the remaining two (Alcohol Dependence and Behavioral Disinhibition). Estimates of the total contribution of genotyped SNPs from GCTA are also given in Table 1. In deriving the GCTA estimates, we followed standard practice by eliminating members of pairs in which the coefficient of relatedness (GRM) was greater than .025 (Yang et al., 2011). This reduced our sample to 3671. Because GCTA is based on differences in genetic resemblance among individuals who are only remotely related, the confidence intervals associated with the estimates are wide. Nonetheless, it is notable that except for the Illicit Drugs phenotype, all of the GCTA estimates are substantially less than the corresponding biometric estimates of a2.
