have a minimum of 2.5 pack-years of smoking. A total of 823 COPD cases and 810 controls were included in the present analysis. All of the subjects used in the primary and replication populations were current or former smokers (Table 1). Although the mean number of pack-years smoked was higher in cases (mean 32 SD 18) compared with controls (mean 19 SD 13), subjects with a range of smoking intensities were included in the analysis. The distribution of pack-years of smoking in cases and controls in the Bergen cohort is shown in Figure S3.
