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.

The data element name and coding have changed over time:

• HCUP nationwide databases
  • Starting in data year 2023, the data element name is PL_NCHS2 and combines the six NCHS categories into two dichotomous groups indicating metropolitan versus non-metropolitan counties.
  • For data years 2013-2022, the data element name is PL_NCHS and includes coding that identifies the six different NCHS categories.
  • Prior to data year 2013, the data element name is PL_NCHS2006 and includes coding that identifies the six different NCHS categories.
• HCUP state databases
  • Starting in data year 2013, the data element name is PL_NCHS and includes coding that identifies the six different NCHS categories.
  • Prior to data year 2013, the data element name is PL_NCHS2006 and includes coding that identifies the six different NCHS categories.

The categorization has changed over time as NCHS released updated versions:

• Starting in 2024 HCUP databases, the classification of counties is specific to the 2023 revision released by NCHS.
• In HCUP databases between 2014 and 2023, the classification of counties is specific to the 2014 revision released by NCHS.
• In HCUP databases between 2005 and 2012, the classification of counties is specific to the 2005 revision released by NCHS.
• This information is not included on the HCUP databases prior to 2005.

Additional information about the NCHS classification scheme is available at https://www.cdc.gov/nchs/data-analysis-tools/urban-rural.html.