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Mortality match with National Death Index

Codes and Frequencies

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For persons age 18+ included in the NHIS during survey years 1986 to 2009 who provided sufficient data for linking (MORTELIG and whose final vital status was judged deceased (MORTSTAT) as of December 31, 2011, MORTNDI indicates that the source of mortality data was the National Death Index (NDI). The NDI is a central database that collects and stores death records from State vital statistics offices. Mortality ascertainment is first attempted through a probabilistic match between NHIS and NDI death certificate records, if there is sufficient identifying data (Social Security number, date of birth, and name). For additional information, see the technical documents from NCHS on the creation and analysis of the NHIS Linked Mortality Files.

Sources of Information on Mortality Status 

The National Health Interview Survey Linked Mortality Files Analytic Guidelines state, "The primary determination of mortality for eligible participants is based upon matching survey records to the NDI. However, NCHS also relies on additional sources of information to determine the mortality status of a survey participant. Other sources include the Social Security Administration, the Centers for Medicare and Medicaid Services, and death certificates. If a source of mortality, other than a NDI record was available, the participant was considered deceased." (p. 4)

Variables that identify these other sources of mortality data are:

  • MORTCMS (Mortality status obtained from Centers for Medicaid and Medicare Services)
  • MORTSSA (Mortality match with Social Security Administration records)

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


MORTNDI is completely comparable over time.


  • 1986-2009: Persons age 18+ eligible for mortality follow-up and assumed dead.


  • 1986-2009


  • 1986-1991, 1993-2009 : MORTWT