Table 5.

Association between incident asthma and measured NO₂ pollution: within-community versus between-community models.

Measured NO2 pollution	No.a	HR (95% CI)b	σ2c	Likelihood ratio test p-valued
Fall–winter	209	1.29 (1.11–1.49)	0.00016
Within-community deviation	209	1.32 (0.91–1.92)	0.00016	> 0.1
Community mean		1.28 (1.09–1.51)
Summer	204	1.27 (1.03–1.57)	0.00020
Within-community deviation	204	0.99 (0.57–1.72)	0.00019	> 0.1
Community mean		1.32 (1.05–1.66)
Annual	196	1.29 (1.07–1.56)	0.00018
Within-community deviation	196	1.31 (0.76–2.26)	0.00019	> 0.1
Community mean		1.28 (1.05–1.57)

^aNumber of subjects varied because of invalid measurements during fall–winter and summer months.

^bWe adjusted models for Hispanic ethnicity, enrollment group, medical insurance coverage, and community annual mean relative humidity, with baseline strata for age and sex. Measured NO₂ pollution estimates are over a 6.2-ppb exposure contrast, which is the average within-community interquartile range for average annual measured NO₂.

^cValues of σ2 are the random-effects variance estimates, which represent the residual variation in asthma incidence attributable to the community cluster after we included all other fixed predictors in the model.

^dLikelihood ratio tests for the null hypothesis that there is no difference between the random-effects models and between/within-community models were not rejected.