Abstract
BackgroundAutomated geocoding of patient addresses for the purpose of conducting spatial epidemiologic studies results in positional errors. It is well documented that errors tend to be larger in rural areas than in cities, but possible effects of local characteristics of the street network, such as street intersection density and street length, on errors have not yet been documented. Our study quantifies effects of these local street network characteristics on the means and the entire probability distributions of positional errors, using regression methods and tolerance intervals/regions, for more than 6000 geocoded patient addresses from an Iowa county.ResultsPositional errors were determined for 6376 addresses in Carroll County, Iowa, as the vector difference between each 100%-matched automated geocode and its ground-truthed location. Mean positional error magnitude was inversely related to proximate street intersection density. This effect was statistically significant for both rural and municipal addresses, but more so for the former. Also, the effect of street segment length on geocoding accuracy was statistically significant for municipal, but not rural, addresses; for municipal addresses mean error magnitude increased with length.ConclusionLocal street network characteristics may have statistically significant effects on geocoding accuracy in some places, but not others. Even in those locales where their effects are statistically significant, street network characteristics may explain a relatively small portion of the variability among geocoding errors. It appears that additional factors besides rurality and local street network characteristics affect accuracy in general.
Highlights
Automated geocoding of patient addresses for the purpose of conducting spatial epidemiologic studies results in positional errors
The simplest model we considered was given by y = + x +e where y represents the magnitude of a positional error, or some transformation thereof; x represents the covariate of interest; a and b are the y-intercept and slope, respectively, of an assumed straight line relating the expectation of y to x; and e represents model error
The effect of street segment length on geocoding accuracy was statistically significant for municipal addresses, for which, as expected, mean error magnitude increased with length
Summary
Automated geocoding of patient addresses for the purpose of conducting spatial epidemiologic studies results in positional errors. In some studies, geocoding is performed by visiting each address with a global positioning (GPS) receiver or by referencing a very accurate (e.g., orthophoto-rectified) image map; it is cheaper and much more common to obtain geocodes by an automated procedure, which uses widely available GIS software to match each address to a street segment georeferenced within a street database (e.g., a U.S Census Bureau TIGER file) and linearly interpolate the position of the address along that segment. This procedure, called automated geocoding, is known as street geocoding.
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