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 = 0.006). Indeed, although the addition of the rs16969968 × peer smoking interaction term increased the explain variance of the overall model (R2) by only 0.5% (18.9% vs. 18.4%) the variance in nicotine dependence attributable to H.S. peer smoking was 4–6 times lower among those with highest risk genotype at rs16969968 than the lower risk genotypes: AA = 2.5%, GA/AG = 11.2%, GG = 14.2%; z = 2.64, p=0.004 and z = 3.27, p = 0.0005 respectively.
