based on CPD) for light or occasional smokers, although we do know they smoked only when they were in specific social circumstances such as during a party or gathering with their friends. Further, the SC status was based on individual self-reports, which were not biochemically verified, and this might lead to potential bias in phenotyping. Nevertheless, we do not feel this bias would greatly affect our results, as the definitions used in the current study have been used in other studies of this type as well [27], [43]. This is especially true for SQ, as it produces significantly more positive findings than any other smoking measures for ND in both linkage and association analyses [43]. Third, we investigated the association of this cluster with three smoking-related phenotypes only in the Korean total and male samples. We did not perform a similar analysis of the female sample because of the small sample size attributable to the small percentage of female smokers (3%), which is the case for many other Asian countries such as China (∼4% of Chinese women aged 15 years or older are smokers [50]). Thus, we could not determine whether this gene cluster has any significant impact on smoking
