substantial genetic correlation between MD and regular smoking in women (ra = 0.56). While a similar estimate has been reported among adolescent females (ra = 0.62, McCaffery et al. 2008), lower estimates have also been reported (ra = 0.17–0.25, Korhonen et al. 2007; Lyons et al. 2008). McCaffery et al. (2008) found that the genetic correlation between these traits was not significant among adolescent males.
