GWAS statistical analyses were performed with software package SAS (SAS Institute Inc., Cary, NC). Genotypic association analysis was conducted with logistic regression for association with “smoking status” and with a Poisson regression analysis for association with “SQ”. Genotypes were treated as independent variables and phenotypes (smoking status and SQ) were treated as dependent variables in each method. To adjust for the effects of “age” or “sex” on the association, these two covariates were included in a model together with the genotype information and the model was compared in terms of likelihood with another restricted model where only the effects of the covariates were estimated. The significance for the covariate-adjusted association, which is the difference in likelihood of the two models, was tested using a chi-square test.
