2008), its role should be carefully examined in international samples where the practice is common (Belanger et al., 2011) even in individuals who do not report cigarette smoking (Belanger et al., 2013; Gage et al., 2014). We also did not query participants about blunt smoking (i.e., rolling marijuana in cigar wrappers, which may contain a small, residual amount of tobacco). The practice of blunt smoking is more common in AA populations but less so in women (Fairman 2015; Timberlake 2013). Fifth, rates of cigarette and cannabis use were somewhat lower in MOFAM, which might have impacted our estimation of C+T as MOFAM was the sole source of nontwin siblings. MOFAM women were somewhat younger than MOAFTS women at their last assessment (22 vs. 25 years, Table 1) and may have been marginally less likely to have surpassed the full risk period for onset of cigarette and cannabis use. This age and sample effect was accounted for in all twin modeling, nonetheless combining a general population cohort of twins with a sample with overrepresentation of high-risk families may have influenced our findings.
