National Health Interview Survey (NHIS) Restricted Variables

If researchers interested in using NHIS data find that something asked on the questionnaires does not have a corresponding variable in the public use data set, that variable may be restricted. The following list is not exhaustive, but it provides examples of NHIS variables that are restricted.


Geography is most often used to add contextual data to NHIS data. The geocodes page lists what geographic codes are available for 1990-current NHIS.

Preliminary Quarterly Microdata Files

Examples of Restricted Variables Used by Other Researchers

  • Country of Birth and Related Immigration Variables (Person File)
  • State and Year of Birth (Person File)
  • Industry and Occupation Codes (Person File before 1997, Sample Adult 1997-present)
  • Detailed Race and Hispanic Origin (Person File)
  • Exact Dates (e.g., date of birth in Person File)

Restricted and Public Use Variable Lists *

*All lists are sorted by question.

More detailed documentation, such as variable values and questionnaire information, for 1997 to the present are available by request. Detailed variable lists are not available for years prior to 1997.If you are interested in receiving the documentation, please contact


Page last reviewed: August 11, 2020, 02:00 PM