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BIRTHYR is a 4-digit-numeric variable.

9997: Unknown-Refused
9998: Not in Universe or Not Ascertained
9999: Unknown-Don't know

BIRTHYR is bottom coded to 84 years before the survey year (e.g. for 1997, bottom code is 1913: birth year 1913 and before; for 1998, bottom code is 1914: birth year 1914 and before).


For all persons, BIRTHYR reports the person's year of birth.

Beginning in 2017, NHIS has suppressed birth year; going forward, this variable is no longer available on public use files.


BIRTHYR is bottom-coded at 1913 in the 1997 NHIS sample to reflect the top-coding of age at 85 years; this bottom-code increased by one year with every annual NHIS sample. Otherwise, there are no comparability issues.


  • 1997-2016: All persons.


  • 1997-2016