title: [Comparison of Google and Yahoo applications for geocoding of postal addresses in epidemiological studies].
abstract: BACKGROUND
  Geocoding is the assignment of geographic coordinates to spatial points, which often are postal addresses. The error made in applying this process can introduce bias in estimates of spatiotemporal models in epidemiological studies. No studies have been found to measure the error made in applying this process in Spanish cities. The objective is to evaluate the errors in magnitude and direction from two free sources (Google and Yahoo) with regard to a GPS in two Spanish cities.
  
  
  METHODS
  30 addresses were geocoded with those two sources and the GPS in Santa Pola (Alicante) and Alicante city. The distances were calculated in metres (median, CI95%) between the sources and the GPS, globally and according to the status reported by each source. The directionality of the error was evaluated by calculating the location quadrant and applying a Chi-Square test. The GPS error was evaluated by geocoding 11 addresses twice at 4 days interval.
  
  
  RESULTS
  The overall median in Google-GPS was 23,2 metres (16,0-32,1) for Santa Pola, and 21,4 meters (14,9-31,1) for Alicante. The overall median in Yahoo was 136,0 meters (19,2-318,5) for Santa Pola, and 23,8 meters (13,6- 29,2) for Alicante. Between the 73% and 90% were geocoded by status as "exact or interpolated" (minor error), where Goggle and Yahoo had a median error between 19 and 23 metres in the two cities. The GPS had a median error of 13.8 meters (6,7-17,8). No error directionality was detected.
  
  
  CONCLUSIONS
  Google error is acceptable and stable in the two cities, so that it is a reliable source for Para medir elgeocoding addresses in Spain in epidemiological studies.
authors.affiliation: Unidad de Investigación de Análisis de la Mortalidad y Estadísticas Sanitarias, Departamento de Enfermería Comunitaria, Medicina Preventiva y Salud Pública e Historia de la Ciencia, Universidad de Alicante, Alicante, España. ja.quesada@ua.es
authors.forename: Jose Antonio
authors.initials: JA
authors.lastname: Quesada
authors.forename: Andreu
authors.initials: A
authors.lastname: Nolasco
authors.forename: Joaquín
authors.initials: J
authors.lastname: Moncho
mesh_terms: D016000:Cluster Analysis; D016021:Epidemiologic Studies; D040362:Geographic Information Systems / Q000592:standards*; D062305:Geographic Mapping; D006801:Humans; D013030:Spain