A total of 4597 twin participants provided blood samples and completed the SSAGA-OZ questionnaire. 2618 families were included in the analysis. Since parents were not genotyped, only families containing a non-identical sibling pair contributed to the “within” test of association. 1177 families included a DZ pair and hence were potentially informative for both the “within” and the “total” test of association. 814 families included an MZ pair and hence contributed information to just the “total” test. Similarly, 627 families had just a single offspring (i.e. trios) and these contributed information to just the “total” test. The mean age of the study population was 43.8 ± 11.5 years, ranging from 26 to 89 years. The mean age of female participants was significantly higher (44.3 vs 42.6) than for males (p = 0.001) (see Table 1). While a small percentage (<3%) of the sample had always abstained from alcohol, the majority (∼93%) had consumed alcohol in the previous year, with 7.6% and 5.5% of male and females, respectively, reporting that they drank alcohol on a daily basis. With respect to alcohol dependence,
