The presence of population stratification among our study subjects was evaluated using a STRUCTURE analysis (18) of 200 SNPs genotyped in our subjects and available for four ethnicities in the HapMap data. Subject ethnicity was plotted in relationship to Central European (CEU), Yoruban in Nigeria (YRI), and Japanese from Tokyo (JPT) and Han Chinese in Beijing (CHB) populations. Individuals found to have less than 85% European ancestry were excluded from the analyses. This resulted in the exclusion of 51 individuals (27 heavy smokers and 24 light smokers). Thus, 1452 heavy smokers and 1395 light smokers were included in the statistical analyses.
