Table 1.

Characteristics of cohort participants at baseline by four categories by quartiles of ${\mathrm{PM}}_{2.5}$ concentration.

Variables	Total	${\mathrm{PM}}_{2.5}$ categorya
		Q1	Q2	Q3	Q4
Participants ($n$)	189,793	58,034	40,243	42,512	49,004
Individual-level
Age (years, $\text{mean}\pm \text{SD}$)	$54.8\pm 10.7$	$54.6\pm 10.5$	$55.2\pm 10.8$	$54.9\pm 10.9$	$54.9\pm 10.7$
Marital status (% of married)	91.0	94.7	91.1	91.8	85.9
Smoking (%)
Never	25.9	22.9	30.0	21.7	29.8
Former	5.9	6.1	4.0	5.7	7.2
Current	68.2	71.0	66.0	72.5	63.0
Years of smoking for current smokers ($\text{mean}\pm \text{SD}$)	$21.8\pm 17.8$	$22.9\pm 17.6$	$21.5\pm 18.3$	$23.1\pm 17.4$	$19.6\pm 17.6$
Years of smoking for former smokers ($\text{mean}\pm \text{SD}$)	$1.7\pm 7.6$	$1.7\pm 7.7$	$1.2\pm 6.3$	$1.6\pm 7.5$	$2.1\pm 8.5$
Cigarettes per day in current smokers	$13.5\pm 13.2$	$13.5\pm 12.7$	$16.5\pm 15.7$	$13.4\pm 12.8$	$11.2\pm 11.4$
Cigarettes per day in former smokers	$1.1\pm 5.1$	$1.1\pm 5.4$	$0.8\pm 4.6$	$1.0\pm 5.1$	$1.2\pm 5.2$
Passive smoking (%)	79.7	83.2	77.1	83.1	74.9
Education, $\le 6\text{years}$ (%)	72.3	70.8	69.6	74.9	70.7
Indoor air pollution (%)
Coal	27.6	29.8	17.8	33.6	27.7
Biomass	35.9	25.0	43.5	45.6	34.1
No exposure	36.5	45.2	38.7	20.8	38.2
Alcohol drinking (%)	32.6	37.4	37.5	26.4	28.4
Amount of alcohol consumed (drinks/week)	$10.7\pm 21.9$	$12.1\pm 22.5$	$16.2\pm 28.4$	$8.0\pm 18.9$	$7.0\pm 15.2$
Occupational exposure (%)	4.5	4.4	3.4	4.0	6.1
Fruit and vegetable consumption (%)	31.8	49.4	20.6	22.6	28.1
BMI (${\mathrm{kg}/\mathrm{m}}^2$, $\text{mean}\pm \text{SD}$)	$21.6\pm 2.6$	$21.3\pm 2.7$	$21.0\pm 2.4$	$21.8\pm 2.5$	$22.1\pm 2.7$
Hypertension (%)	26.9	24.9	22.5	31.3	29.2
Area-level factors
Urban (%)	20.2	13.7	19.3	17.2	31.2
Region
Northeast (%)	10.2	31.3	3.2	0.0	0.0
North (%)	8.8	2.1	6.6	24.5	4.6
Northwest (%)	11.3	5.7	0.0	38.4	3.6
Southwest (%)	20.7	26.6	22.9	4.2	26.2
South-central (%)	41.1	20.5	67.4	27.6	55.9
East (%)	7.9	13.8	0.0	5.4	9.7
Mean years of education ($\text{mean}\pm \text{SD}$)b	$7.8\pm 1.2$	$7.4\pm 1.2$	$7.6\pm 1.0$	$8.0\pm 1.0$	$8.3\pm 1.4$
Number of deaths
Nonaccidental	50,022	15,466	10,348	13,263	13,779
CVD	18,859	4,797	3,567	5,433	5,062
COPD	11,989	4,231	2,043	2,754	2,961
Lung cancer	2,523	797	452	579	695
Age-adjusted mortality rate (per 100,000 person-years)		2,538	2,355	3,077	2,695

^aQuartile cutpoints of ${\mathrm{PM}}_{2.5}$ concentrations were based on mean exposures during 2000–2005 at each baseline cohort site. Minimum, $4.23{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; 25th percentile, $28.3{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; 50th percentile, $38.9{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; 75th percentile, $60.1{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; maximum, $83.8{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$.

^bArea-level mean years of education.