NCHS Urban-Rural Classification Scheme for Counties

National Center for Health Statistics (NCHS) data systems are often used to study the associations between urbanization level of residence and health and to monitor the health of urban and rural residents. NCHS has developed a six-level urban-rural classification scheme for U.S. counties and county-equivalents. The most urban category consists of "central" counties of large metropolitan areas and the most rural category consists of nonmetropolitan "noncore" counties. Two versions of the NCHS scheme are available: 1) the 2006 NCHS Urban-Rural Classification Scheme for Counties (based on the Office of Management and Budget's 2000 standards for defining metropolitan and micropolitan statistical areas, the December 2005 delineation of these areas, and Vintage 2004 postcensal estimates of the resident U.S. population) and 2) the 1990 census-based NCHS Urban-Rural Classification Scheme for Counties (based on the Office of Management and Budget's 1990 standards for defining metropolitan statistical areas, the June 1993 delineation of these areas, and 1990 census data).

The levels of the NCHS scheme were chosen for their utility in studying health differences across the urban-rural continuum. The NCHS scheme has more metropolitan levels (four) than nonmetropolitan levels (two) because the large U.S. metropolitan population (in 2000, about 83% of the U.S. population) can support more levels for health analyses than the relatively small nonmetropolitan population. Because of differences between the 2000 and 1990 Office of Management and Budget metropolitan-nonmetropolitan classification, some of the classification rules used to assign counties to the six levels of the 2006 NCHS scheme differ from those used to make assignments for the 1990 census-based NCHS scheme. However, the basic framework of both schemes is the same.

A key feature of the NCHS urban-rural scheme, which makes it particularly well-suited for health analyses, is that it separates counties within large metropolitan areas (1 million or more population) into two categories: large "central" metro (akin to inner cities) and large "fringe" metro (akin to suburbs). This is an important feature of the NCHS urban-rural scheme because for a number of health measures, residents of large fringe metro areas fare substantially better than residents of other urbanization levels. For these measures, residents of the inner cities and suburbs of large metropolitan areas must be differentiated to obtain an accurate characterization of health disparities across the full urban-rural continuum.

The report NCHS Urban–Rural Classification Scheme for Counties [PDF - 1.3 MB] details development of the 2006 NCHS scheme and provides some examples of the scheme's application to mortality data and to health measures from the National Health Interview Survey. The report also describes the 1990 census-based NCHS scheme.

Use of the Urban-Rural Classification with Natality and Mortality Files

The NCHS Urban-Rural Classification Scheme for Counties should only be used with data files where all counties are identified. Standard mortality and natality public-use files do not identify counties with populations less than 100,000. Specifically, the county FIPS codes for counties with populations less than 100,000 are not provided on these files; instead all of these counties are assigned the same geographic code for “balance of state.” Because there are counties with populations less than 100,000 in all of the urban-rural categories except the large central metro category, it is not possible to compute birth and death rates by urbanization level using the standard natality and mortality public-use files. Access to mortality and natality files with all counties identified currently requires NCHS approval of the project and the signing of a data user’s agreement.