The heritability estimates for AD obtained in our models were slightly lower than observed in prior analyses of this sample (Kendler et al., 1992; Prescott and Kendler, 1999; Prescott et al., 1999), probably because we excluded lifetime abstainers from the current analyses. Because there is a small genetic effect on who uses alcohol, excluding the abstainers reduces the genetic variance observed in AD and AC. Nonetheless, our heritability estimates are broadly consistent with other comparable population based (Heath et al., 1997; Hrubec and Omenn, 1981; Kendler et al., 1997) and clinically ascertained twin cohorts (Pickens et al., 1991). This increases the likelihood that our results will generalize to other samples but this needs to be confirmed by future studies.
