Relation between prevalence of COPD to smoking of subjects Smoking status Subject (5220) COPD (310) OR (95% CI) p n% Non smoking 3051 110 3.6 ref Smoking 2169 200 9.2 2.72 (2.14 - 3.45) < 0.001 Waterpipe 1221 122 10.0 2.97 (2.27 - 3.88) < 0.001 Cigarette 472 36 7.6 2.21 (1.50 - 3.26) < 0.001 Two kinds 476 42 8.8 2.59 (1.79 - 3.74) < 0.001 Comments: smoking affected COPD by 2.72 (2.14 - 3.45) times than the non-smoking.