A cohort study evaluating the risk of stroke associated with long-term exposure to ambient fine particulate matter in Taiwan

Table 1 Descriptive characteristics of the study cohort at baseline in 2011 and the health outcomes

	Study cohort, N = 1,362,284
Variable	n	%
Age, years
20–44	735,384	54.0
45–64	495,520	36.4
65–74	82,146	6.0
75+	49,234	3.6
Mean (SD)	44.0	(15.2)
Men	659,112	48.4
Urbanization level
1 (most urbanized)	359,435	26.4
2	606,694	44.5
3	232,680	17.1
4–7	163,475	12.0
Income level, Taiwan dollars^a
< =272,470	432,566	31.8
272,471–273,351	369,701	27.1
273,351–311,566	338,977	24.9
> 311,566	221,040	16.2
Comorbidity^b
Diabetes	80,181	5.9
Hypertension	171,447	12.6
Hyperlipidemia	113,536	8.3
Coronary artery disease	42,894	3.2
Chronic obstructive pulmonary disease	55,700	4.1
Atrial fibrillation	4054	0.3
Outcomes and follow-up
Person-years at risk
Total	8,019,765
Mean (Median)	5.9 (6.0)
Number of events (Incidence)^c
Total stroke	12,942 (1.6)
Ischemic stroke	9919 (1.2)
Hemorrhagic stroke	3023 (0.4)

Abbreviation: N number of study subjects, SD standard deviation
Data are n (%) unless otherwise noted
^aper Capita Disposable Income
^bPatients with at least one inpatient or two outpatient claims with a diagnosis of the comorbid conditions in two years before the index date
^cIncidence per 1000 person-years

ISSN: 1476-069X