In contrast to the AOS findings, there was no evidence for association between AOI and any of the SNPs examined in the CHRNA5/A3/B4 cluster. It might be intuitively expected that AOI and AOS would be highly correlated and that the associations with risk SNPs would not vary between them greatly even though there are differences in statistical power between AOI and AOS due to sample size. However, the correlations between AOI and AOS among the samples where both measures are available are actually rather low (ranging from 0.20–0.65, data not shown). There is additional support for the hypothesis that a low correlation exists between these two phenotypes. Breslau et al. (1993) showed the lag time from first cigarette to daily smoking onset was significantly longer in those who initiated <14 years of age relative to those initiating ≥17 years of age. A social explanation was proposed for these findings in that early initiators were said to face a nonpermissive environment (e.g. availability, community norms, adult supervision, etc.) [Breslau et al., 1993]. In addition, we performed an ad hoc exploratory analysis
