PL_NCHS is a six-category urban-rural classification scheme for U.S. counties developed by the National Center for Health Statistics (NCHS) especially for use in health care research. The classification emphasizes urban distinctions and is unique in differentiating between central and fringe counties of large metropolitan areas. Smaller metropolitan counties are subdivided by population. Non-metropolitan counties are divided simply into micropolitan and non-core categories.

The county classifications are based on the Office of Management and Budget (OMB) metropolitan/micropolitan assignments. These assignments were refined using information from the Rural-Urban Continuum Code (RUCC) and Urban Influence Code (UIC) of the Economic Research Service of the U.S. Department of Agriculture and county characteristics from the Census Bureau population estimates.

Although the six NCHS categories may conceptually be mapped into the four categories of the PL_UR_CAT4 classification used elsewhere in HCUP, the two schemes are not entirely compatible. A few counties are categorized differently in the two schemes because they are based on inconsistent population estimates produced on different dates.

The name of this HCUP data element and the version of the categorization have changed over time:

• Starting in 2014 HCUP databases, the classification of counties is specific to the 2014 revision released by NCHS.
• Starting in the 2013 HCUP databases, the data element name is PL_NCHS.
• Between 2005 and 2012, the data element name was PL_NCHS2006 and the classification of counties was specific to the 2005 revision released by NCHS.
• This information was not included on the HCUP databases prior to 2005.

Additional information about the NCHS classification scheme is available on the Internet at http://www.cdc.gov/nchs/data_access/urban_rural.htm .