Lifetime diagnoses (binary) of comorbidities were obtained from the SSAGA. Conduct disorder or antisocial personality disorder (depending on age; ASP) and cannabis dependence or abuse (CAN) diagnoses were measured using DSM-IV criteria (American Psychiatric Association, 1994). We operationally defined lifetime frequent tobacco use (TOB) as someone having smoked a total of at least 100 cigarettes over their lifetime (Bondy et al., 2009) and having a >0 score on the Fagerström Test for Nicotine Dependence (FTND; Heatherton et al., 1991), as some people consider themselves non-smokers even when they have consumed >100 cigarettes in a lifetime (Pomerleau et al., 2004). FTND was assessed with a lifetime timeframe, and thus is inclusive of ex-smokers. Absence of frequent tobacco use was defined as non-smokers, or someone with >100 lifetime cigarettes with a zero on FTND. Because FTND was not administered during the early phase of COGA data collection, a separate yes/no question from the SSAGA (“Have you ever smoked cigarettes daily for a month or more?”) was substituted to define frequent tobacco use for those without the FTND data. Lifetime major depressive disorder (MDD) was determined with DSM-IV (American Psychiatric Association, 1994) or DSM-III-R criteria (American Psychiatric Association, 1987).
