title: Positional accuracy and geographic bias of four methods of geocoding in epidemiologic research.
abstract: OBJECTIVE
  We examined the geographic bias of four methods of geocoding addresses using ArcGIS, commercial firm, SAS/GIS, and aerial photography. We compared "point-in-polygon" (ArcGIS, commercial firm, and aerial photography) and the "look-up table" method (SAS/GIS) to allocate addresses to census geography, particularly as it relates to census-based poverty rates.
  
  
  METHODS
  We randomly selected 299 addresses of children treated for asthma at an urban emergency department (1999-2001). The coordinates of the building address side door were obtained by constant offset based on ArcGIS and a commercial firm and true ground location based on aerial photography.
  
  
  RESULTS
  Coordinates were available for 261 addresses across all methods. For 24% to 30% of geocoded road/door coordinates the positional error was 51 meters or greater, which was similar across geocoding methods. The mean bearing was -26.8 degrees for the vector of coordinates based on aerial photography and ArcGIS and 8.5 degrees for the vector based on aerial photography and the commercial firm (p < 0.0001). ArcGIS and the commercial firm performed very well relative to SAS/GIS in terms of allocation to census geography. For 20%, the door location based on aerial photography was assigned to a different block group compared to SAS/GIS. The block group poverty rate varied at least two standard deviations for 6% to 7% of addresses.
  
  
  CONCLUSIONS
  We found important differences in distance and bearing between geocoding relative to aerial photography. Allocation of locations based on aerial photography to census-based geographic areas could lead to substantial errors.
authors: Division of Health Behavior Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63108, USA. mschootm@im.wustl.edu
authors: Mario
authors: M
authors: Schootman
authors: David A
authors: DA
authors: Sterling
authors: James
authors: J
authors: Struthers
authors: Yan
authors: Y
authors: Yan
authors: Ted
authors: T
authors: Laboube
authors: Brett
authors: B
authors: Emo
authors: Gary
authors: G
authors: Higgs
mesh_terms: D001249:Asthma / Q000453:epidemiology; D015982:Bias; D002648:Child; D004812:Epidemiologic Methods; D040362:Geographic Information Systems; D006801:Humans; D011204:Poverty Areas; D015203:Reproducibility of Results; D017062:Small-Area Analysis; D019371:Topography, Medical / Q000379:methods*