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Eligibility status for mortality follow-up

Codes and Frequencies

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MORTELIG indicates whether participants in the NHIS during survey years 1986 to 2014 were eligible for follow-up by linkage to National Death Index (NDI) records. Only persons who were age 18+ at the time of interview and who provided sufficient data were eligible for linking to the NDI and eligible for inclusion in the public use files (IPUMS NHIS code 1 in MORTELIG). Linked mortality data for children (IPUMS NHIS code 2) are not available from the NHIS public use files; researchers interested in these data or in material with additional detail should review the documentation for the restricted access NHIS Linked Mortality Files. Adults with insufficient data for matching (IPUMS NHIS code 3) could not be linked to the NDI to create mortality variables.

Linking of Death Records to NHIS participants 

The NCHS website provides the following description of the NDI:

The National Death Index (NDI) is a central computerized index of death record information on file in the State vital statistics offices. Working with these State offices, NCHS established the NDI as a resource to aid epidemiologists and other health and medical investigators with their mortality ascertainment activities. [The NDI is] [a]vailable to investigators solely for statistical purposes in medical and health research.

The NCHS has assisted researchers by linking the records for NHIS survey participants with the NDI. The mortality variables in the NHIS public use files (and in IPUMS NHIS) are based on results from probabilistic matches between NHIS records and NDI death certificate records. The NCHS website explains:

Linkage of the NHIS survey participants with the NDI provides the opportunity to conduct studies designed to investigate the association of a variety of health factors with mortality, using the richness of the NHIS questionnaires.

For additional information, see the technical documents from NCHS on the creation and analysis of the NHIS Linked Mortality Files.

Appropriate Weights 

Because adult survey participants who provided insufficient data for linking may differ from those who provided enough data for linking, ignoring the ineligible adult respondents (IPUMS NHIS code 3 in MORTELIG) could lead to biased mortality analysis. To correct this bias, NCHS developed eligibility-adjusted weights: MORTWT, available for 1986-2014, for use with variables from the NHIS person files, and MORTWTSA, available for 1997-2014, for use with variables from the sample adult files. When analyzing NHIS variables from the person files in conjunction with mortality variables, users should employ MORTWT (rather than the standard person weight, PERWEIGHT). When analyzing variables from the sample adult files in conjunction with mortality variables, users should employ MORTWTSA (rather than the standard sample weight, SAMPWEIGHT).

Related Variables
For a list of the other mortality variables included in the IPUMS NHIS, please refer to the MORTSTAT variable description.


MORTELIG is completely comparable across years.


  • 1986-2014: All persons.


  • 1986-2014