In order to illustrate more clearly the risk for nicotine dependence based on the combined genetic and environmental risk factors, we present in Figure 1 estimates from a multivariate logistic regression model for rs16969968. Using the group with higher quartiles of parent monitoring and lowest risk genotype (GG) as the reference group, Figure 1 displays the odds ratios for varying levels (higher quartiles vs. lowest quartile) of parent monitoring combined with genetic risk levels of rs16969968 (GG, GA, AA). Proceeding from the left panel with lowest risk genotype (GG) to the right panel with highest risk genotype (AA), we observe the pattern of increased genetic risk indicated by the dotted broken lines. Further, the right panel shows that the effects of the risk genotype (AA) were not homogeneous across levels of parent monitoring. The genetic risk was markedly increased in the lowest quartile of parent monitoring, compared with higher levels of parent monitoring.
