Prior to 2007, the HCUP data element name for this variable was misspelled PL_NHCS2006. Beginning with the 2007 data, the data element is accurately named PL_NCHS2006.
NCHS2006 is a simplified, six-category, county-level scheme developed by the National Center for Health Statistics for use in studying the association between urbanization and health. This scheme is unique in emphasizing differences within metropolitan areas.
The NCHS scheme combines aspects of the 2003 versions of the Rural-Urban Continuum Codes (RUCC) and the Urban Influence Codes (UIC). The metropolitan counties are subdivided into three categories by population. The over one million group is further subdivided into Central and Fringe categories as defined by OMB standards. Non-metropolitan counties are divided simply into micropolitan and non-core categories.
Additional information about the UIC classification scheme is available on the Internet at http://www.cdc.gov/nchs/r&d/rdc_urbanrural.htm.