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Last Edited: 3/28/2008

Post office box addresses: a challenge for geographic information system-based studies
Written: Jul 2003

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.

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Suggested Citation

  • Hurley S, Saunders T, Nivas R, Hertz A, Reynolds P.  Post office box addresses: a challenge for geographic information system-based studies.  Epidemiology, 14(4):386-391, July 2003.