Figure 2From: Genetic susceptibility for chronic bronchitis in chronic obstructive pulmonary disease The quantile–quantile plots for the three-cohort meta-analysis including 1000 Genomes project imputed data for (A) COPD subjects with chronic bronchitis (CB) versus smoking controls and (B) CB versus no CB within COPD subjects, after adjustment for age, sex, pack-years of cigarette smoking and genetic ancestry using principal components. Back to article page