In the current report, we examine a large population-based sample of Swedish twins to assess whether MD, regular tobacco use and ND are influenced by shared genetic and/or environmental factors. We employ a modified version of the causal–contingent–common pathway (CCC) model (Kendler et al. 1999) to account for the contingency of ND on regular tobacco use. We fit models to cigarette use and cigarette-related ND in both males and females; snus (smokeless tobacco) use was sufficiently prevalent among males to also fit models addressing the relationship between MD, regular snus use and snus-related ND.
