Two primary outcome measures are used in analyses reported here: (1) a quantitative alcohol consumption factor score (ACFS) (Agrawal et al. 2009; Grant et al. 2009); and (2) a binary DSM-IV diagnosis of alcohol dependence. Individuals who denied any lifetime alcohol use were coded as missing for the alcohol consumption measure and for alcohol dependence. Respondents who endorsed at least 3 of 7 diagnostic criteria in a single year were given a DSM-IV alcohol dependence diagnosis. The ACFS was created from four indices of alcohol consumption queried in the alcohol use disorders section: (1) lifetime maximum 24 hour alcohol consumption (log-transformed to adjust for skewness); and for the heaviest drinking period of at least one year’s duration, (2) weekly alcohol consumption (log-transformed); (3) frequency of drinking to intoxication; (4) frequency of drinking ≥5 drinks per day. Because the NAG sample is enriched for heavy smokers, data from BigSib, a general community sample ascertained from the Australian Twin Registry on the basis of large sibship size [see (Saccone et al. 2007) for more information] were used to generate scoring coefficients more
