National Death Index

The National Death Index (NDI) is a computerized index of information compiled by the National Center for Health Statistics (NCHS) from death record information submitted to the NCHS by the state offices of vital statistics. This national file of death records contains a standard set of identifying information for each decedent, which includes first and last names, middle initial, father's surname, social security number, sex, race, date of birth, state of birth, state of residence, marital status, and age at death.

The NDI enables investigators to ascertain if the participants in their studies have died by matching the identifying information for an individual with the NDI database. The NDI Retrieval Program searches the NDI file to identify possible matches between a particular NDI death record and a particular user record. An NDI match can identify the state in which death occurred, the date of death, and the death certificate number. To qualify as a possible match, both records must satisfy at least one of seven criteria. The complete social security number alone would provide a match; the other six matching criteria consist of various combinations of birth date, name, and father's surname. When a user record matches one or more NDI records, an NDI Retrieval Report is generated, listing all the identifying information for each of the possible matches, and indicating items that match exactly, items that do not match, and items that possibly match. However, it is up to the users to determine whether NDI records match the individuals in their studies.

In designing a study in which ascertaining death might be important, investigators should collect as many of the NDI data items as possible to optimize the assistance available through the NDI. Using NDIPlus, investigators can obtain the ICD-9 codes for the cause of death (underlying cause and multiple causes). The NDI does not provide copies of death certificates.

The NDI database contains death record information (beginning with 1979 deaths) for all 50 states, the District of Columbia, Puerto Rico, and the Virgin Islands. Death records are added to the NDI file annually, about 12 months after the end of each calendar year. Approximately 2 million death records are added each year. Deaths during the 2005 calendar year will be available for the NDI search in April 2007.

Use of the NDI is restricted to statistical purposes involving medical and health research. Investigators planning to use the NDI must complete an application and review process, which usually takes 2 to 3 months. Users must meet confidentiality requirements and must submit data on study subjects in a manner that meets the NCHS technical specifications. The fees for routine NDI searches, as of June 2007, consist of a $350 service charge, plus $0.21 per study subject for each year of death searched if vital status of subject is unknown, and $5.00 per decedent if subjects are known to be deceased. Fees for the optional NDIPlus are slightly higher. A free user's manual can be requested from the NDI; it includes a sample application form.