Predisposing risk of each significant SNP was evaluated by an odds ratio (OR) and a corresponding 95% confidence interval (CI), which was calculated using the software package Stata (Stata Corporation, College Station, Texas). To calculate an OR for a certain SNP, subjects were first divided into two genotype groups, carriers of a minor allele (i.e., homozygotes of the minor allele and heterozygotes) and non-carriers of the minor allele (i.e., homozygotes of the major allele). The OR was then calculated by comparing the prevalence of smokers (i.e., ratio of smokers vs. non-smokers) in the two genotype groups.
