The prevalence of lifetime MD in the SALT sample has been described elsewhere (Kendler et al. 2006). Prevalence of MD, regular tobacco use and ND levels, along with measures of sex differences where appropriate, are provided in Table 1. Mean age at onset of MD was 39.2 years. Mean age of onset of tobacco use was 18.0 years. Additional details are provided in Supplementary Table 1 and Materials.
