Table 1.

Baseline characteristics of study subjects.

Variable	Total COPD	Pure COPD	ACO	P-value
	6,313	3,186 (50.5)	3,127 (49.5)	$0{.4577}^a$
Follow-up period (years)	4.9 ± 0.5	4.9 ± 0.5	4.9 ± 0.5	$0{.7633}^b$
Average PM10 exposure (10 μg/m3)
12 months	48.2 ± 5.7	48.1 ± 5.7	48.2 ± 5.7	${0.4160}^b$
6 months	41.2 ± 5.1	41.1 ± 5.2	41.2 ± 5.1	${0.2742}^b$
3 months	39.5 ± 5.2	39.4 ± 5.3	39.5 ± 5.2	${0.4531}^b$
1 month	46.4 ± 6.1	46.5 ± 6.0	46.4 ± 6.2	${0.7554}^b$
Sex				$0{.0064}^a$
Men	3386 (53.6)	1763 (55.3)	1623 (51.9)
Women	2927 (46.4)	1423 (44.7)	1504 (48.1)
Age groups				$<0{.0001}^a$
40~49 years	1478 (23.4)	835 (26.2)	643 (20.6)
50~59 years	1971 (31.2)	1007 (31.6)	964 (30.8)
60~69 years	2144 (34.0)	1025 (32.2)	1119 (35.8)
70 years +	720 (11.4)	319 (10.0)	401 (12.8)
Smoking status
Never-smokers	3348 (53.0)	1678 (52.7)	1670 (53.4)	$0{.6121}^a$
Former smokers	967 (15.3)	502 (15.8)	465 (14.9)
Current smokers	1998 (31.7)	1006 (31.6)	992 (31.7)
Body mass index (kg/m2)	23.9 ± 3.3	23.8 ± 3.3	24.0 ± 3.4	$0{.0025}^b$
Charlson Comorbidity Index	2. 1 ± 1.6	1.9 ± 1.6	2.2 ± 1.5	$<0{.0001}^b$
Income levels				$0{.1102}^a$
0	180 (2.9)	89 (2.8)	91 (2.9)
0–10%	540 (8.6)	249 (7.8)	291 (9.3)
10–20%	440 (7.0)	218 (6.8)	222 (7.1)
20–30%	462 (7.3)	221 (6.9)	241 (7.7)
30–40%	508 (8.1)	245 (7.7)	263 (8.4)
40–50%	552 (8.7)	268 (8.4)	284 (9.1)
50–60%	571 (9.0)	286 (9.0)	285 (9.1)
60–70%	678 (10.7)	349 (11.0)	329 (10.5)
70–80%	687 (10.9)	361 (11.3)	326 (10.4)
80–90%	828 (13.1)	425 (13.3)	403 (12.9)
90–100%	867 (13.7)	475 (14.9)	392 (12.5)

p-value^a for Chi square. p-value^b for T test.

Data is presented as mean ± SD or number (%).