In general, our estimates for the heritability of regular smoking and cigarette-based ND are comparable with those from the Virginia Twin Registry (a2 = 0.80 for regular use and 0.67 for ND) (Maes et al. 2004), although in that sample variance could be constrained to be equal across the sexes. Heritability specific to dependence is also similar across the studies (a2 = 0.26 for the Virginia sample v. 0.37 for Swedish males and 0.30 for Swedish females).
