Table 3. Other potential factors related to the risk of COPD.

Variables	Control (n = 3479)	COPD (n = 490)	OR (95% CI)	P
Exposure to the second-hand smoking (hrs/week)
<7	2955(84.9)	387(79.0)	1.50(1.18–1.90)	0.001
7-	524(15.1)	103(21.0)
Cough without a cold
No	3091(88.9)	419(85.5)	1
Yes	388(11.2)	71(14.5)	1.35(1.03–1.77)	0.031
Shortness of breath
No	2530(72.7)	178(36.3)	1
Yes	949(27.3)	312(63.7)	4.67(3.83–5.70)	<0.001
Long-term exposure to dust or chemical particles
No	2964(85.2)	303(61.8)	1
Yes	515(14.8)	187(38.2)	3.55(2.89–4.36)	<0.001
History of chronic respiratory diseases during childhood
No	3174(91.2)	349(71.2)	1
Yes	305(8.8)	141(28.8)	4.20(3.35–5.28)	<0.001
BMI (kg/m2)
28-	419(12.04)	48(9.8)	1
24-	1357(39.01)	164(33.47)	1.05(0.75–1.48)	0.758
<24	1703(48.95)	278(56.73)	1.42(1.03–1.97)	0.032