. Author manuscript; available in PMC: 2011 Sep 28.

Published in final edited form as: Stat Med. 2010 Jan 15;29(1):116–129. doi: 10.1002/sim.3732

Table 1.

Summary (R² and P-value) of association between NO₂ and alternative measures of traffic exposures using GIS and ADT for roadways within a 750 ft buffer of residence.

Traffic exposure measure	Unweighted¹		Distance weighted²

	R²	P-value	R²	P-value
ADT on nearest road³	.017	.1527	.018	.1449
Highest ADT in buffer	.105	.0003	.044	.0220
ADT sum for all segments	.115	.0002	.069	.0040
Integrated exposure model (isotropic) using step function dispersion	-	-	.510	<.0001
Integrated exposure model (anisotropic): SW Cubic spline and constants for others	-	-	.513	<.0001

Measure is unadjusted for distance.

Measure is weighted using distance in meters to residence and the corresponding Gaussian dispersion weights used in other studies, $W_{i} = exp {- d^{2} / 7432.24} / (0.4 \sqrt{2 π})$ . [1,27]

Alternative transformations of distance were considered, include the log [4], but R² was not substantially improved.