We further tested our GWAS sample for population stratification using the genomic control method (25). Based on genome-wide SNP information, we estimated the inflation factor (λ), a measure for population stratification. Ideally, for a homogeneous population with no stratification, the value of λ should be equal to or near 1.0. For our total sample, the estimated λ value was 1.009 for smoking status and 1.012 for cigarette consumption (SQ), suggesting essentially no population stratification; these findings further confirm the results achieved through the Structure 2.2 software.
