National Death Index
NATIONAL DEATH INDEX
The National Death Index (NDI) was implemented in 1982 to facilitate retrospective and prospective studies in medical and health research by reducing the time, expense, and effort involved in ascertaining information about deaths, either for an entire study population or just for those subjects who could not be contacted. The NDI is a national, computerized index of death record information compiled from computer files submitted to the National Center for Health Statistics (NCHS) by each state's vital statistics office. The NDI contains records on virtually all deaths in the United States since 1979. About 2.4 million death records are added to the file each year.
A researcher or investigator desiring access to NDI data must submit an official application form. (The NDI is not accessible to organizations or the general public for legal, administrative, or genealogy purposes.) Once the application is approved, the investigator is instructed to submit a computer file containing identifying information on each study subject. This file is to be prepared in a specified format and then mailed to NCHS on diskette or CD-ROM. Investigators are strongly encouraged to compile as many of the NDI data items as possible: first and last name, middle initial, father's surname, Social Security number, date of birth, state of birth, state of residence, sex, race, marital status, and age at death (if known). NCHS searches this information against records in the NDI database and sends the investigator a report showing which records generated one or more possible matches with NDI records. The NDI also provides the state of death and the death certificate number for each possible match. It is the investigator's responsibility to assess the match results and to determine which are true matches based on the data items that agree or disagree. The investigator may then contact state vital statistics offices for copies of the relevant death certificates to confirm the matches or obtain information such as the cause of death.
Beginning in 1997, the NCHS obtained authorization from each state vital statistics office to enhance the NDI service by also releasing the cause of death codes for close matches. This new service is called NDI Plus. The codes are derived from the World Health Organization's International Classification of Diseases for both the underlying and multiple causes of death.
The NDI has been used for a variety of studies, including occupational health studies where workers exposed to hazardous chemicals or low-level radiation are tracked over time. It has been used for tracking participants in cohort studies of health problems and clinical trials of new treatments; for tracking subjects of cancer registries to determine outcomes; and for the U.S. National Longitudinal Mortality Study, where a sample of over 2 million persons drawn from Census Bureau surveys are tracked over time.
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