Table 3.

Estimated HR for the incidence of chronic respiratory diseases per 10 μg/m³ increase of PM_2.5 by stratified Cox proportional hazards models.

Characteristics	All-cause chronic respiratory disease				CB
	No. of onset	HRs	95% CI	Pinteraction value	No. of onset	HRs	95% CI	Pinteraction value
Age	482			0.35	276			0.19
< 60	303	1.31	1.11–1.54		178	1.32	1.06–1.64
≥ 60	179	1.04	0.83–1.29		98	1.08	0.80–1.45
Gender				0.77				0.92
Male	300	1.27	1.08–1.50		166	1.32	1.06–1.65
Female	182	1.09	0.88–1.35		110	1.03	0.78–1.36
Education level				0.43				0.76
< High school	287	1.23	1.04–1.46		171	1.37	1.09–1.71
≥ High school	194	1.02	0.83–1.26		104	0.95	0.72–1.26
Monthly income				0.22				0.68
< 500 CNY	188	1.15	0.93–1.43		108	1.28	0.96–1.70
≥ 500 CNY	294	1.14	0.96–1.34		168	1.15	0.92–1.43
Smoking status				0.28				0.16
No	246	1.08	0.90–1.30		144	1.07	0.84–1.36
Yes	236	1.23	1.02–1.50		132	1.37	1.06–1.76
Passive smoking status				0.44				0.38
No	234	1.09	0.90–1.31		147	1.16	0.91–1.47
Yes	242	1.22	1.01–1.46		127	1.02	1.00–1.03
Alcohol intake				< 0.001				< 0.001
No	310	0.99	0.84–1.17		181	0.98	0.79–1.22
Yes	172	1.52	1.21–1.91		95	1.79	1.31–2.44
Physical activity				0.34				0.60
No	310	1.13	0.91–1.40		106	1.11	0.83–1.49
Yes	172	1.14	0.97–1.35		170	1.23	0.99–1.52

Abbreviations: HR, hazard ratio; CI, confidence interval; CB, chronic bronchitis; COPD, chronic obstructive pulmonary disease.

Covariates: adjusted for age, sex, BMI, smoking status (yes or no), education level (below high school or high school or higher), personal income ( < 500 CNY and ≥ 500 CNY per month), smoking status (yes or no), passive smoking status (yes or no), alcohol intake (yes or no), physical activity (yes or no), family history of related chronic respiratory diseases (yes or no), and city (Rizhao, Shenyang, Taiyuan, and Tianjin).

P_interaction values are the interaction results between PM_2.5 and the variables.