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Evaluation of Geocoding Quality in Montana

This study assesses geocoding accuracy in Montana’s cancer registry, identifying areas with PO box-only cases and potential census tract misclassification. Results show county and census tract variations, guiding future improvements for sub-county analysis.

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Evaluation of Geocoding Quality in Montana

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  1. Evaluation of Geocoding Quality in Montana Considerations for Sub-county analysis Heather Zimmerman

  2. Background • Montana Central Tumor Registry (MCTR) routinely geocodes address at diagnosis using the NAACCR geocoder • 16% of cases have only PO Box reported • 2.5% have incomplete or incorrect physical address

  3. Evaluation Questions • What areas of Montana have the highest proportion of cases with PO box only? • What areas have the highest potential of census tract misclassification?

  4. Methods • Analysis included all cases of invasive cancer diagnosed from 2003 to 2016 among Montana residents. • GIS coordinate Quality (item #366) grouped into 3 categories • Street level or better: codes 00-05 • Zip code or city centroid: codes 06-09 and 11 • PO box zip centroid: code 10 • Cases with codes 98 “Unknown” (only 12 cases) were excluded from analysis • There were no cases with codes 12 “County centroid” or 99 “Unmatchable”

  5. Results

  6. Results: Year of Diagnosis

  7. Results: By County • Percent of cases geocoded to the street level or better varies widely between counties • 95.1% in Yellowstone • 26% in Prairie • Median is 69.5%

  8. Results: By County

  9. Results: By Census Tract • There is even more variation at the census tract level • 0% to 96.5% for census tracts

  10. Results: By Census Tract

  11. Results: By Census Tract

  12. Cancer Incidence Analysis in Butte

  13. Let’s take another look at Butte

  14. Another Example

  15. Conclusions • Our most rural areas have the highest proportion of cases with PO box only • Urban areas have the highest potential for census tract misclassification

  16. Next Steps • Reduce the number of cases with PO box only • Working with Montana Cancer Registrar’s Association to identify quality improvement projects to get physical address for residents with a PO Box • Use ZCTA for sub-county analysis when timeframe is limited to available population data • Carefully assess GIS coordinate quality before doing analysis at the census tract level

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