Ever-smoking, Caucasian subjects with at least moderate COPD (GOLD stage II or higher) from four independent cohorts (NETT,18 ECLIPSE,19 GenKOLS cohort from Bergen, Norway,20 and COPDGene (first 1000 subjects)21) were studied (Table 1). In total 3,441 subjects had at least 1 (out of 4) non-missing, smoking-related phenotype (Table 1). All phenotypes were self-reported using either Case Report Form (smoking status and the lifetime average CPD in the ECLIPSE cohort) or modified versions of the American Thoracic Society/Division of Lung Diseases Respiratory Disease Questionnaire.22 Since current smokers were not eligible for the NETT study, this cohort did not contribute to the analyses on smoking cessation and current CPD.
