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 of mortality 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)

Other variables identifying the sources of mortality information are:

• MORTCMS (Mortality status obtained from Centers for Medicaid and Medicare Services)

• MORTNDI (Mortality match with National Death Index)

The NDI is a central database that collects and stores death records from State vital statistics offices. As noted above, 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.