A summary of previous reports of genetic correlations between MD and tobacco use traits is provided in Table 5. Our estimate of the genetic correlation between MD and regular smoking in females is substantially lower than has been previously reported in adult (Kendler et al. 1993) and adolescent (McCaffery et al. 2008) females. Our results for males are comparable with (but lower than) other reports of genetic correlations between MD and regular smoking. Our estimate of the genetic correlation between MD and cigarette-based ND is substantially lower than that reported by Lyons et al. (2008). This discrepancy may be partially attributable to their use of a dichotomous rating of ND, whereas the current report used five categories of dependence derived from the FTND; these scales might measure different aspects of ND (Hughes et al. 2004; Kandel et al. 2005).
