COPD prevalence of the subjects Subjects Commue Total (n = 5220) COPD (n = 310)% p Kien Thiet 2540 177 7.0 < 0.01 Kien Bai 2680 133 5.0 Total 5220 310 5.9 Comments: prevalence of COPD was 5.9% (Kien Thiet 7.0% vs Kien Bai 5.0%).