All three parent studies (Begleiter et al., 1995; Bierut et al., 2007, 2008; Nurnberger, Jr. et al., 2004) used modified versions of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) to assess substance use and substance use disorders (Bucholz et al., 1994). The current analyses utilized data on nicotine and cannabis related measures. For nicotine, these included smoking initiation (defined as smoking 100 or more cigarettes during the lifetime; while this is also referred to as regular smoking, we use the term “smoking initiation” to be consistent with prior meta-analyses of this phenotype), current tobacco use (currently using tobacco or last using a tobacco product within the year prior to the interview) and cigarettes smoked per day (CPD), defined as a categorical variable (0=10 cigarettes or less; 1=11-20; 2=21-30; 3=31 or more). Those who did not report smoking initiation were coded as missing for current smoking and CPD. For cannabis, items included ever using cannabis, current use (currently using cannabis or last using cannabis with the year prior to the interview) and DSM-IV cannabis abuse/dependence, with lifetime never users coded as missing for current use and abuse/dependence.
