Table 3.

Hazard Ratios^a Associated With Categorical Exposures to PM_2.5 in a Cohort of Actively Employed US Aluminum Workers, Stratified by Facility Type, 1998–2012

Exposure Category, mg/m3, by Facility Type	Traditional Cox Modelb		Cox MSM/IPWc
	HR	95% CI	HR	95% CI
Smelting facilities
<0.260	1.00	Referent	1.00	Referent
0.260–1.469	1.51	0.98, 2.37	2.00	1.16, 3.45
1.470–1.959	1.73	1.06, 2.86	1.97	1.06, 3.67
1.960–2.589	1.53	0.97, 2.45	1.78	1.00, 3.18
≥2.590	1.53	0.97, 2.46	1.77	1.01, 3.11
Fabrication facilities
<0.07	1.00	Referent	1.00	Referent
0.07–0.139	1.34	0.96, 1.88	1.35	0.96, 1.88
0.140–0.219	1.29	0.90, 1.87	1.18	0.83, 1.69
0.220–0.369	1.29	0.89, 1.86	1.31	0.90, 1.89
≥0.370	1.31	0.92, 1.89	1.23	0.87, 1.75

Abbreviations: CI, confidence interval; HR, hazard ratio; IPW, inverse probability weight; MSM, marginal structural model; PM_2.5, particulate matter with aerodynamic diameter of 2.5 μm or less.

^a Observations below the 10th percentile of exposure are the reference group.

^b Cox models with attained age as time scale, including covariates for sex, race, smoking status, body mass index (weight (kg)/height (m)²), job grade, plant, and risk score. Baseline hazards based on decade of age.

^c Cox models with attained age as time scale fitted in a pseudopopulation created by use of inverse probability weights, including covariates for sex, race, smoking status, body mass index, job grade, and plant. Baseline hazards based on decade of age.