Do you calculate your hospital market share by ZIP Code or by County? Come to find out even if your answer is 'by county'; you are likely using ZIP Codes.
When patients register at a hospital, physician's office, surgery center or outpatient imaging center, their address is provided with ZIP code, not county. Many state data programs crosswalk the ZIP Codes to counties in order to create an additional view into the data.
How are ZIPs crosswalked into Counties?
There are a few methods of converting ZIP codes into county. Three common methods are geographic centroid, population centroid and geographic mass.
The method your data source utilizes is important to understand, so you can better understand what population is included and excluded in your data and intelligence.
Counties are a great way to organize ZIP Codes as long as the organization recognizes that the analysis is on ZIP Codes and not purely county boundaries. Another way to organize ZIP Codes is by geographic area. Organize the primary service area into five sections: downtown or center, southeast, northeast, northwest and southwest. After the primary service area is divided, do the same with the secondary service area. Organizing services in this manner may be more meaningful than by county.
So the next time someone is requesting a county-based service area and the data does not include county, you will know you can crosswalk the ZIP codes to counties and be ready to move forward.