Documentation for the URBRRL variable says it is determined based on the NCHS 2013 classification scheme. How is this applied to counties after 2020? I.e. in the 2021 data, are 2020 counties classified using the 2013 scheme with older CBSA designations? Or are they still using old county boundaries? Thanks in advance!
For the 2016-current NHIS data, the metropolitan area definitions are those that became effective with the 2013 NCHS Urban–Rural classification scheme. This NCHS documentation on geocodes*, for a given NHIS sample design period (e.g., 2016-forward), the geographic data in the NHIS such as state, county, census tract, etc. come from the decennial census prior to the beginning of the sample design period (in this case, 2010 decennial census). NCHS expects to publish an update of the NCHS Urban-Rural Classification Scheme for Counties in 2025 (and later, the NHIS).
*Note that while this documentation focuses on restricted-use versions of the data that include more detailed geographic identifiers than are in the public-use data, it contains relevant information on geocodes in the NHIS more broadly.
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