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For sample persons under 18 years old in 1981 and all persons in 1982 and forward, BIRTHMO reports the person's month of birth. According to personal communication between IPUMS NHIS and NHIS staff, releasing month of birth on the public use files was determined by staff at the National Center for Health Statistics to pose a disclosure risk. Person's month of birth was suppressed on the public use files beginning in 2015.


There are no comparability issues.


  • 1981: Sample persons under age 18.
  • 1982-2014: All persons.


  • 1981-2014