title: Accuracy of residential geocoding in the Agricultural Health Study.
abstract: BACKGROUND
  Environmental exposure assessments often require a study participant's residential location, but the positional accuracy of geocoding varies by method and the rural status of an address. We evaluated geocoding error in the Agricultural Health Study (AHS), a cohort of pesticide applicators and their spouses in Iowa and North Carolina, U.S.A.
  
  
  METHODS
  For 5,064 AHS addresses in Iowa, we compared rooftop coordinates as a gold standard to two alternate locations: 1) E911 locations (intersection of the private and public road), and 2) geocodes generated by matching addresses to a commercial street database (NAVTEQ) or placed manually. Positional error (distance in meters (m) from the rooftop) was assessed overall and separately for addresses inside (non-rural) or outside town boundaries (rural). We estimated the sensitivity and specificity of proximity-based exposures (crops, animal feeding operations (AFOs)) and the attenuation in odds ratios (ORs) for a hypothetical nested case-control study. We also evaluated geocoding errors within two AHS subcohorts in Iowa and North Carolina by comparing them to GPS points taken at residences.
  
  
  RESULTS
  Nearly two-thirds of the addresses represented rural locations. Compared to the rooftop gold standard, E911 locations were more accurate overall than address-matched geocodes (median error 39 and 90 m, respectively). Rural addresses generally had greater error than non-rural addresses, although errors were smaller for E911 locations. For highly prevalent crops within 500 m (>97% of homes), sensitivity was >95% using both data sources; however, lower specificities with address-matched geocodes (more common for rural addresses) led to substantial attenuation of ORs (e.g., corn <500 m ORobs = 1.47 vs. ORtrue = 2.0). Error in the address-matched geocodes resulted in even greater ORobs attenuation for AFO exposures. Errors for North Carolina addresses were generally smaller than those in Iowa.
  
  
  CONCLUSIONS
  Geocoding error can be minimized when known coordinates are available to test alternative data and methods. Our assessment suggests that where E911 locations are available, they offer an improvement upon address-matched geocodes for rural addresses. Exposure misclassification resulting from positional error is dependent on the geographic database, geocoding method, and the prevalence of exposure.
authors.affiliation: Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, 9609 Medical Center Drive, Rockville, MD, USA. rena.jones@nih.gov.
authors.forename: Rena R
authors.initials: RR
authors.lastname: Jones
authors.forename: Curt T
authors.initials: CT
authors.lastname: DellaValle
authors.forename: Abigail R
authors.initials: AR
authors.lastname: Flory
authors.forename: Alex
authors.initials: A
authors.lastname: Nordan
authors.forename: Jane A
authors.initials: JA
authors.lastname: Hoppin
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Hofmann
authors.forename: Honglei
authors.initials: H
authors.lastname: Chen
authors.forename: James
authors.initials: J
authors.lastname: Giglierano
authors.forename: Charles F
authors.initials: CF
authors.lastname: Lynch
authors.forename: Laura E
authors.initials: LE
authors.lastname: Beane Freeman
authors.forename: Gerard
authors.initials: G
authors.lastname: Rushton
authors.forename: Mary H
authors.initials: MH
authors.lastname: Ward
mesh_terms: D000383:Agriculture / Q000706:statistics & numerical data*; D015331:Cohort Studies; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data*; D005260:Female; D062305:Geographic Mapping; D006304:Health Status; D006801:Humans; D007484:Iowa / Q000453:epidemiology; D008297:Male; D009657:North Carolina / Q000453:epidemiology; D010575:Pesticides; D011446:Prospective Studies
chemical_list: D010575:Pesticides