For the association analyses COPD affection status in the Norway discovery cohort, we used a logistic regression model to perform single-marker genotype trend tests for the QC-passed SNPs. To control for the possibility of spurious associations resulting from population stratification, we used a modified EIGENSTRAT method [29] (and Text S1). This showed that there were 12 significant principal component axes, all of which were included in the model. We included age and sex, and since smoking effects are known to influence COPD risk, we also included current smoking status and pack-years of smoking as co-variates.
