Table 3.

Significant Factors for Development of COPD

	Univariate Analysis			Multivariate Analysis
	HR	95% CI	P-value	HR	95% CI	P-value	VIF
Low FEF25-75%* †	5.665	3.156–10.166	<0.001	3.308	1.650–6.632	<0.001
Sex (male)	1.616	0.941–2.777	0.082
Age (years)	1.038	1.009–1.068	0.009	1.088	1.050–1.128	<0.001	1.254
BMI (kg/m2)	0.927	0.844–1.017	0.108
Co-morbidity
Hypertension	1.668	0.975–2.856	0.062
Diabetes	1.504	0.817–2.770	0.190
CHD	1.077	0.387–2.993	0.887
Previous CVA	1.088	0.264–4.489	0.907
RE, PUD, or GERD	1.074	0.385–2.993	0.892
Depression	2.979	1.337–6.639	0.008	1.550	0.674–3.566	0.302	1.057
History of tuberculosis	1.063	0.564–2.001	0.850
Smoking status**
(reference: never smoked)
Occasional smoker	2.242	0.968–5.195	0.060	4.586	1.913–10.993	<0.001	1.166
Long-term smoker	2.003	1.118–3.586	0.020	2.179	1.115–4.258	0.023	1.379
PFT
FEV1 z-score	0.743	0.620–0.890	0.001
FVC z-score	0.875	0.743–1.030	0.109
FEV1/FVC z-score	0.284	0.182–0.444	<0.001	0.452	0.219–0.936	0.033	2.034
FEF25-75% z-score	0.366	0.256–0.523	<0.001	0.453	0.267–0.766	0.003	1.882

Notes: ^†Adjusted for age, depression, smoking status, and FEV1/FVC z-score. *Low FEF_25-75%: FEF_25-75% z-score below −0.8435 (the optimal cut-off value for predicting COPD development). **Occasional smoker: an adult who has smoked less than 20 pack-years in his or her lifetime; long-term smoker: an adult who has smoked over 20 pack-years in his or her lifetime.

Abbreviations: BMI, body mass index; CHD, coronary heart disease; CI, confidence interval; CVA, cerebrovascular accident; FEF, forced mid-expiratory flow; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; GERD, gastroesophageal reflex disease; HR, hazard ratio; PFT, pulmonary function test; PUD, peptic ulcer disease; RE, reflux esophagitis; VIF, variance inflation factor.