The first of these unanswered questions concerns potential sex differences. Rates of problematic drinking behavior are typically greater in males (Kendler et al. 2007), and exist even when rates of alcohol use do not differ between sexes. In related research, studies have reported sex differences in alcoholic subtypes, reporting an excess of women in internalizing subtypes and an excess of men in externalizing subtypes (Carpenter and Hasin, 2001; Epstein et al., 2002; Moss et al., 2007). Whether there are sex differences in the genetic influences on alcohol use disorders across development is less clear since studies conducted on one sex, or that examine mean levels of drinking collapsed across sexes, may mask these effects. Second, the men in Kendler’s study made retrospective reports of their past drinking at a mean age of 40. Several studies suggest that there are important recall biases in self-reports of past drinking behavior (Engels et al. 1997.; Labouvie et al. 1997). Accordingly, examining these effects with prospective alcohol use data would circumvent the recall biases. Third, previous studies have also indicated that other aspects of
