16.2.11 Geography

If the level of reporting is best described by the geography of the individual/service, use one of the following two tables. Specifically, if the geography of the reporting is based on the residence of the individual, use the “Residence Geography”. If the geography of the reporting is based on the location of service, use the “Service Geography”. Also see Appendix I for details on scoring scenarios involving the overlap of Insurance Coverage, Expected Payer/Public Assistance and Means-Tested Programs, and Geography.

Table 24: Residence Geography Scoring

Characteristics	Score
State or geography with population >2,000,000	-5
Population 1,000,001 - 2,000,000	-3
Population 560,001 - 1,000,000	-1
Population 250,001 - 560,000	0
Population 100,001 - 250,000	+1
Population 50,001 - 100,000	+3
Population 20,001 - 50,000	+4
Population 4,001- 20,000	+5
Population ≤ 4,000	+7

Table 25: Service Geography Scoring

Characteristics	Score
State or geography with population >2,000,000	-5
Population 1,000,001 - 2,000,000	-4
Population 560,001 - 1,000,000	-3
Population 250,001 - 560,000	-1
Population of reporting region 20,001 - 250,000	0
Population of reporting region ≤20,000	+1
Address (Street and ZIP)	+3
Address in rural area	+5
Address in frontier area	+7

The Geography score, while it may or may not represent the denominator of the table, does provide a reference to the base population about which the reporting is occurring. This will often be reflected in the title of the table if a statewide table. Otherwise, the geography may be represented in the rows or columns. There are two different scoring sets based on whether the geography reporting is based on the residence of the individual to which the information applies or to the service location.

The scores are higher for geography related to residence address because so much information is publicly available about individuals and their address of residence. For large populations greater than 560,000, which is equivalent to the size of a state, there is a negative score because the size of the denominator masks the individual. The number 560,000 was chosen as a cut-off because this is the size of the smallest state (Wyoming). We chose to use the cut-off at the smallest state’s population because state level reporting is not listed as one of the 18 identifiers in the HIPAA Safe Harbor method.

The scores for the service geography are lower because clients can generally come from diverse locations for services. Although people often seek services or have health conditions close to their homes, they may also travel extensive distances. Reviewers do need to make sure that there are no constraints associated with services that would mean the service geography and resident geography are the same. For example, if a program publishes service utilization by county and the county services can only be used by county residents, then the service utilization by county is also the county of residence. Scoring should be based on the criteria that result in the highest score and, thus, the highest risk.

There are smaller areas within counties where the population is significantly lower than the overall county population. One example of this is census tracts, which are small, relatively stable statistical subdivisions of a county or an equivalent statistical entity. These tracts can be updated by local participants before each decennial census through the Census Bureau’s Participant Statistical Areas Program (PSAP). Census tracts typically cover contiguous areas, but their size can vary widely based on population density. The boundaries of these tracts are designed to remain unchanged over time, allowing for consistent statistical comparisons from one census to the next. Generally, census tracts have populations ranging from 1,200 to 8,000 people, with an optimum size of population around 4,000. To account for the higher re-identification risk associated with smaller populations, a score of +7 is assigned when the population size is 4,000 or fewer in the residential area.

Service Geography includes a level of detail that is identified as “Address (Street and ZIP).” This deals with reporting by provider (hospital, clinic, provider office, etc.) Provider addresses are public information and are public at the street address level. A given provider will tend to have a standard catchment area or the geographic boundaries from which most patients come from. This information is published by the Department of Health Care Access and Information (previously the Office of Statewide Health Planning and Development - OSHPD) for hospitals. While this addresses where most patients or clients come from, patients or clients may also come from outside the catchment area. For that reason, this does not score as high as the more detailed geography under Residence Geography.

However, addresses associated with rural and frontier areas have a higher re-identification risk due to lower population density per square mile and isolation of communities in these areas. Thus, higher scores are assigned for Providers’ addresses, except where the Provider is defined as Hospital, in rural and frontier areas.