Research
Comparing a single-stage geocoding method to a multi-stage geocoding method: how much and where do they disagree?
-
* Corresponding author: Gina S Lovasi gl2225@columbia.edu
1 Columbia University, Institute of Social and Economic Research and Policy, New York, NY, USA
2 University of Washington, Cardiovascular Health Research Unit, Seattle, WA, USA
3 Washington State Department of Health, Olympia, WA, USA
4 University of North Carolina, Departments of Epidemiology and Medicine, Chapel Hill, NC, USA
5 University of Washington, Department of Biostatistics, Seattle, WA, USA
6 University of Washington, Departments of Epidemiology, Medicine, and Health Services, Seattle, WA, USA
International Journal of Health Geographics 2007, 6:12 doi:10.1186/1476-072X-6-12
Published: 16 March 2007Abstract
Background
Geocoding methods vary among spatial epidemiology studies. Errors in the geocoding process and differential match rates may reduce study validity. We compared two geocoding methods using 8,157 Washington State addresses. The multi-stage geocoding method implemented by the state health department used a sequence of local and national reference files. The single-stage method used a single national reference file. For each address geocoded by both methods, we measured the distance between the locations assigned by each method. Area-level characteristics were collected from census data, and modeled as predictors of the discordance between geocoded address coordinates.
Results
The multi-stage method had a higher match rate than the single-stage method: 99% versus 95%. Of 7,686 addresses were geocoded by both methods, 96% were geocoded to the same census tract by both methods and 98% were geocoded to locations within 1 km of each other by the two methods. The distance between geocoded coordinates for the same address was higher in sparsely populated and low poverty areas, and counties with local reference files.
Conclusion
The multi-stage geocoding method had a higher match rate than the single-stage method. An examination of differences in the location assigned to the same address suggested that study results may be most sensitive to the choice of geocoding method in sparsely populated or low-poverty areas.