Testing all possible interactions among variables in the main effects model, significant interactions were found between H.S. peer smoking and both rs16969968 and gender (p = 0.0077 & p=0.002, respectively; see Table 2). The two-way interaction rs16969968 × gender was not significant (p = 0.32) nor was the three-way interaction peer smoking × rs16969968 × gender (p = 0.67), and the point estimates of the peer smoking by rs16969968 were similar by gender (female OR =0.94; male OR=0.91). H.S. peer smoking appeared to have stronger effects on nicotine dependence for males than for females (OR = 1.37 95% CI 1.29 – 1.46 vs. OR = 1.20 95% CI 1.14 – 1.26). To illustrate the peer smoking by rs16969968 interaction figure 1 presents the predicted probabilities of nicotine dependence for number of peer smokers by rs16969968 genotype, adjusted for gender and age. The overall risk of nicotine dependence is highest for the rs16969968 AA genotype but H.S. peer smoking had a substantially lower impact on those with this genotype compare to those with the GA or GG genotypes combined (p =
