Few studies have examined the relationship between MD and smokeless tobacco use. Sihvola et al. (2008) explored early (age 14 years) depressive disorders and later (age 17.5 years) cigarette use or smokeless tobacco use in a Finnish population, and found similar odds ratios for both types of tobacco use. Those findings are generally in agreement with our own. Schmitt et al. (2005) investigated cigarette and smokeless tobacco use in the male sample of the Virginia twin study and reported heritability estimates similar to those reported here for both regular cigarette use (a2 = 0.69 for males in the current study versus 0.64 by Schmitt et al.) and snus use (a2 = 0.66 v. 0.73).
