The analysis was restricted to individuals who had reached young adulthood (19 years or older) because we were interested in transitions to daily smoking and advanced smoking behaviors, outcomes that often occur during this time. In the COGA adolescent and young adult study, 1,209 European ancestry individuals with a last interview age of 19 years or older were genotyped for the CYP2A6 variants, and participants for the analyses were drawn from this group (Figure 1). The sample used to analyze daily versus non-daily smokers consisted of 776 individuals who had initiated smoking (64% of all subjects). For transitions to advanced smoking behaviors, we focused on the sample of 506 daily smokers (65% of initiators, 42% of all subjects, described in Table 1).
