Although general population studies consistently find that males have higher rates of substance use and dependence than females (Kessler, Chiu, Demler, Merikangas, & Walters, 2005; Kessler, et al., 1994; Stinson, et al., 2005; Teesson, Hall, Lynskey, & Degenhardt, 2000; Warner, Kessler, Hughes, Anthony, & Nelson, 1995), these sex differences may be less marked amongst a sample distinguished by high levels of antisocial or externalising problems. There is evidence of a heritable liability for antisocial behaviour, and the polygenic multiple threshold model suggests that females may need a greater liability to express antisocial behaviour (Rhee, Waldman, Rhee, & Waldman, 2002). Therefore the women in the current sample may carry a higher genetic and/or environmental liability for antisocial behaviour (ASB) than the males. Greater environmental liability for females has already been noted in the form of more dysfunctional families and exposure to more unfavourable social factors (Chatham, et al., 1999; Chiang, et al., 2007). Alternatively, there may be sex differences in gene-environment interactions or gene-environment correlation (Rutter, et al., 2006).
