Assessments were performed using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA), which gathers detailed information on substance use with high reliability and validity (Bucholz et al., 1994; Bucholz et al., 1995; Hesselbrock et al., 1999). Smoking initiation was evaluated with the question “Have you ever smoked a full cigarette?” Daily smoking was defined as smoking at least 4 days per week for at least a month as done in previous analyses (Kapoor et al., 2012). This was assessed among individuals who had initiated smoking using the questions “When you were smoking regularly, how many days per week did you usually smoke cigarettes?” and “For how long did you smoke this many cigarettes at that rate?”
