Smoking quantity was assessed with cigarettes smoked per day (CPD). The primary phenotype for analysis was a dichotomous trait contrasting light smoking controls (CPD≤10) to heavy smoking cases (CPD>20). In addition, a 4-level ordered trait (CPD≤10; 11≤CPD≤20; 21≤CPD≤30; CPD≥31 coded as 0, 1, 2, 3 respectively) was developed for confirmatory analysis. The only exception was one study (Women’s Health Initiative) that measured smoking amount with different threshold levels (CPD≤14, 15≤CPD≤24, 25≤CPD≤34, CPD≥35), and CPD≤14 defined the light smoking controls which was contrasted with CPD 25 as heavy smoking cases.
