Participants were selected from the ongoing Nicotine Dependence in Teens (NDIT) study [1], based on ethnicity, smoking status, and provision of a blood or saliva sample for DNA extraction and CYP2A6 genotyping. A total of 610 Caucasian adolescents were genotyped for CYP2A6; 308 Caucasian adolescents who were either smokers at baseline or initiated smoking during follow-up were retained for analysis. Data on sociodemographic variables and smoking behaviors were collected in self-report questionnaires administered every 3-4 months between 1999 and 2004. All participants were asked about their cigarette smoking behaviours using 2 indicators: 1. “Check the one box that describes you best: I have never smoked a cigarette, even just a puff; I have smoked cigarettes, even just a puff, but not at all in the past 12 months; I smoked cigarettes once or a couple of times in the past 12 months; I smoke cigarettes once or a couple of times each month; I smoke cigarettes once or a couple of times each week; I smoke cigarettes everyday”, and 2. A recall of cigarette use in each of the 3
