Table 3.

Univariate and multivariate analysis for COPD

Variables	Univariate analysis			Multivariate analysis
	OR	95% CI	P-value	OR	95% CI	P-value
Sex			<0.001			<0.001*
Male	Reference			Reference
Female	0.230	0.173–0.306		0.234	0.144–0.378
Age	1.080	1.067–1.094	<0.001	1.089	1.068–1.110	<0.001*
Resident district			0.006			0.601
Urban	Reference			Reference
Suburban/rural	1.781	1.181–2.685		1.137	0.701–1.845
Type of residence			<0.001			0.387
General type	Reference			Reference
Apartment	0.518	0.379–0.707		0.855	0.598–1.222
Household income			<0.001
Lowest quartile (Q1)	Reference			Reference		0.806
Low-middle quartile (Q2)	0.578	0.425–0.785		0.931	0.622–1.392
High-middle quartile (Q3)	0.490	0.335–0.716		1.137	0.709–1.823
Highest quartile (Q4)	0.338	0.225–0.507		1.043	0.633–1.718
Educational level			<0.001			0.354
Below elementary	Reference			Reference
Middle school	0.720	0.524–0.988		0.873	0.550–1.386
High school	0.440	0.308–0.629		0.810	0.512–1.280
Above university	0.286	0.192–0.424		0.601	0.346–1.046
Occupation						0.529
Professional job	Reference		<0.001	Reference
Office job	1.755	0.786–3.918		2.009	0.906–4.455
Service and sales	0.762	0.342–1.697		0.805	0.322–2.012
Agriculture and fisheries	3.996	2.015–7.927		1.153	0.504–2.641
Technician	2.401	1.213–4.785		1.242	0.573–2.694
Laborer	2.502	1.309–4.784		1.230	0.538–2.814
Jobless	2.410	1.365–4.256		1.092	0.534–2.233	0.001*
Smoking history			<0.001
Never smoker	Reference			Reference
Light smoker	2.329	1.641–3.305		1.435	0.925–2.227
Medium smoker	3.711	2.528–5.450		2.192	1.305–3.680
Heavy smoker	9.612	6.368–14.511		2.894	1.641–5.102
Nutrition						0.648
Retinol intake (μg)	0.998	0.996–0.999	0.005	1.000	0.999–1.001	0.001*
Vitamin C intake (mg)	0.996	0.995–0.998	<0.001	0.998	0.996–0.999

Note:

^*P<0.05 obtained by multivariate logistic regression analysis.

Abbreviations: OR, odds ratio; CI, confidence interval.