Table 4 provides parameter estimates for the top findings derived from the interaction model. In addition to presenting parameter estimates from regression models that treat AOS as a continuous variable, we also present results of post-hoc analyses in which the sample was divided based on the median value for AOS (age 16). This latter set of analyses was largely conducted for illustrative purposes; i.e., to facilitate examination of differences in odds ratios between earlier and later onset smokers. The sample split with AOS of 16 or lower comprised 562 cases and 280 controls while the split with AOS of 17 or higher comprised 219 cases and 500 controls. In addition to being the sample median, this split-value corresponds to the dichotimization threshold utilized in a previous analysis of SNP x AOS interactions (Weiss et al. 2008). Main effect odds ratios were computed separately for the two sample halves. This approach, unlike the primary analyses, makes no assumptions about the scale of the putative interaction variable (i.e., does not assume that genetic effect sizes scale multiplicatively with AOS). Parameter estimates indicate
