title: Post office box addresses: a challenge for geographic information system-based studies.
abstract: BACKGROUND
  Geographic information system (GIS)-based health studies require information on the physical location of data points, such as subject addresses. In a study of California women diagnosed with breast cancer between 1988 and 1997, we needed to locate the residential addresses of 4,537 women with post office boxes (POBs).
  
  
  METHODS
  We investigated the feasibility of tracing street addresses for the POBs and examined potential selection biases and case attribute misclassifications introduced by different methods of handling POBs in GIS-based health studies.
  
  
  RESULTS
  Our tracing method yielded street addresses for only 34% of POBs in our study. Examination of subjects' case characteristics revealed that boxholders were not representative of the full population. Geocoding using a POB's delivery-weighted five-digit zip code centroid, as a proxy for street address, resulted in case attribute misclassification for 81% of boxholders.
  
  
  CONCLUSIONS
  Disease registries should modernize their infrastructure to complement GIS technologies. Epidemiologists should understand GIS data limitations and consider potential biases introduced by incomplete or inaccurate geocoding.
authors.affiliation: Public Health Institute, Oakland, CA, USA.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hurley
authors.forename: Theresa M
authors.initials: TM
authors.lastname: Saunders
authors.forename: Rachna
authors.initials: R
authors.lastname: Nivas
authors.forename: Andrew
authors.initials: A
authors.lastname: Hertz
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology; D016021:Epidemiologic Studies; D005260:Female; D040362:Geographic Information Systems; D006801:Humans; D008875:Middle Aged; D011177:Postal Service / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity