Smokers were instructed to abstain from smoking approximately 12 hours prior to a deprived session. Abstinence ≥12 hr was reported on 82.5% of the deprived sessions. In 17.5% of the deprived sessions, smokers reported being abstinent between 10 to 12 hr but were included in the analyses because they met the CO criteria. A 10-ppm CO cut-off value was used to verify self-reported abstinence. Average CO levels during deprivation sessions for this subset of the main sample were within this range (M=9.3, SD=5.4 versus M=23.1, SD=10.3 for non-deprivation sessions). No significant differences in average CO levels were noted between genotypes. Because a significant percentage (approximately 32%) of the overall sample smoked over a pack a day, we allowed for the possibility that CO values above 10 ppm could occur even after 10 to 12 hr of deprivation. Thus, smokers exceeding the 10-ppm cut-off range were permitted to participate in the session if they reported at least 10 hr of deprivation and their CO value was less than 50% of their baseline CO (4.3 % of the main study sample). Analyses
