Table 5.

Means and the Proportions of All Variables (Potential Confounders) and Their Absolute Standardized Differences Prior to and Following Matching With Propensity Scores Based on PM_2.5 Levels

Variable	Prior to Matching			Following Matching
	Mean		Absolute Standardized Difference	Mean		Absolute Standardized Difference
	Low PM2.5 (< 12 µg/m3)	High PM2.5 (≥ 12 µg/m3)		Low PM2.5 (< 12 µg/m3)	High PM2.5 (≥ 12 µg/m3)
Dew point, K	279.64	281.61	0.43	281.22	281.19	0.01
Black	0.05	0.10	0.30	0.07	0.08	0.11
Female	0.54	0.56	0.28	0.55	0.55	0.03
White	0.90	0.86	0.23	0.90	0.89	0.08
Native American	0.01	0.00	0.19	0.00	0.00	0.03
Air temperature, K	286.81	287.5	0.15	287.19	287.06	0.03
Asian	0.01	0.01	0.11	0.01	0.01	0.03
Ever smoking	0.46	0.46	0.11	0.46	0.46	0.04
Median household income, $	48,188.19	45,793.69	0.11	46,798.2	46,824.52	0.00
Older adults aged ≥ 85 y	0.13	0.13	0.02	0.13	0.13	0.02
Hispanic	0.01	0.01	0.01	0.01	0.01	0.03

Black, white, Asian, Hispanic, and Native American mean the proportion of different racial groups; female means the proportion of female subjects; older adults ≥ 85 years means the proportion of older adults aged ≥ 85 years among Medicare enrollees in each ZIP code; and ever smoking means the proportion of ever smokers in each ZIP code obtained from the Behavioral Risk Factor Surveillance System. See Table 2 legend for expansion of abbreviation.