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Codes and Frequencies

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SEX indicates whether the person was male or female.

Starting in 2019, "Unknown-refused" and "Unknown-don't know" responses are allowed. Prior to 2019, SEX is not coded as "unknown" for any persons included in the IPUMS NHIS data.

According to the 2020 Survey Description, for some variables, including SEX, the 2020 responses of sample adults that were part of the 2020 longitudinal sample were overwritten with their 2019 responses "to mitigate disclosure risks associated with differences in response from repeated measures among the same Sample Adults" (33). The sample adults' actual 2020 responses can be accessed through a Research Data Center (RDC). For more information on the 2020 longitudinal sample, please see SALNGPRTFLG.


Comparability is affected by changes including the 2019 redesign. For 1968 forward, SEX, for most persons, was inferred from the individual's first name or reported relationship to the head of the household. If there was any doubt (e.g., when the respondent gave a name for a household member--such as Marion or Lynn--that is used for both males and females), interviewers were to ask the person's sex (i.e., "Is [FULLNAME] male or female?").

Beginning in 1998, the survey instrument explicitly directed interviewers to "enter your best guess" when the respondent either did not know or refused to answer the direct question about the person's sex that was asked in ambiguous cases. Beginning in 1998, a check item related to SEX was included in the Basic Module, Family Core questionnaire that asked respondents to verify whether their reported sex was correct.

Because explicit questions about the individual's sex were only asked in ambiguous cases, it is unlikely that the presence or absence of these additional directions to fieldworkers compromises the comparability of the SEX variable over time.

The NHIS questionnaire was substantially redesigned in 2019 to introduce a different data collection structure and new content. For more information on changes in terminology, universes, and data collection methods beginning in 2019, please see the user note.


  • 1963-2018: All persons.
  • 2019-2022: Sample adults age 18+ and sample children age 0-17.


  • 1963-2022