In cross-sectional analyses, FEV1/FVC and FEV1 were tested for association with SNP genotypes using a one degree-of-freedom additive model of the dosage value (estimated reference allele count with a fractional value ranging from 0 to 2.0) as a predictor in linear regression models. Associations were examined overall and stratified into ever and never smokers. Overall models were adjusted for age, sex, standing height, smoking status (current/past/never), and pack-years of smoking. Current, past, or never smoking was based on questionnaire responses, and pack-years were calculated for current and past smokers by multiplying smoking dose (packs/day) and duration (years). Stratified models used the same covariates as the overall models, except that the ever-smoker stratum included adjustment for smoking status as current/past and the never-smoker stratum included no smoking-related covariates. Additional study-specific covariates included recruitment cohort (FHS), recruitment center (ARIC and CHS), and principal component eigenvalues for population stratification adjustments (10 components for ARIC and statistically significant components for FHS). Models were implemented using ProbABEL71 in ARIC, R72 in CHS, linear mixed effects models with fixed effects for SNPs and random effects for
