What to know
- There are 4 types of National Death Index (NDI) searches.
- Every search type returns the date of death, state of death, and death certificate number for all matches. NDI Plus searches also return the cause of death.
- NDI users should submit as much information as possible about each study subject when requesting data.
Search types
There are 4 types of National Death Index (NDI) searches. Search costs vary by search type. Fees for the NDI Plus service are slightly higher.
Types of searches
- Researcher doesn't know if subjects are deceased
- Results provide date of death, state of death, and death certificate number
- Results do not provide any cause of death information
- Part of NDI Plus service
- Researcher doesn't know if subjects are deceased
- Results provide date of death, state of death, and death certificate number
- Results provide cause of death information in International Classification of Diseases (ICD) format
- Part of NDI Plus service
- Researcher knows all subjects are deceased
- Results provide date of death, state of death, and death certificate number
- Results provide cause of death information in ICD format
- Part of NDI Plus service
- Limited to researchers who already have information from the death certificate
- Results provide the ICD codes used to identify the cause of death on the death certificate
Search criteria
Researchers use the NDI retrieval program to search for NDI files. The program rejects any user records that don't have sufficient information about data variables used to qualify and identify a match.
Sufficient data variables to qualify
To avoid a possible rejection, user records must satisfy one of the following qualifying conditions or matching criteria—
- FIRST and LAST NAME and SOCIAL SECURITY NUMBER
- FIRST and LAST NAME and MONTH and YEAR OF BIRTH
- SOCIAL SECURITY NUMBER and DATE OF BIRTH and SEX
Sufficient data variables to identify a match
A search of the NDI file will identify possible record matches between individual NDI data records and individual data records submitted by the user.
To qualify as a possible record match, submitted records must satisfy at least one of the following conditions or matching criteria. The specified data fields must match on both the submitted record and the NDI record—
- Social Security number.
- Exact month & +/- 1 birth year, first and last name.
- Exact month & +/- 1 birth year, first and middle initials, last name.
- Exact month & day of birth, first and last name.
- Exact month & day of birth, first and middle initials, last name.
- Exact month & year of birth, first name, father's surname.
- For female subjects: Exact month and birth year, first name, last name (on user's record), and father's surname (on NDI record).
Search results
Requested NDI file years are searched to determine whether a particular NDI death record is a possible record match with a particular study subject record.
NDI returns the date of death, state of death, and death certificate number for all matches to the researcher. Researchers who have purchased the NDI Plus service also receive all causes of death listed on the death certificate, for all "true matches." If there is disagreement with the identified true match, the cause of death may be provided for your identified alternates. Cause of death information is provided in ICD format.
Increase your chance of matches
NDI users are encouraged to submit all information listed above that is available. Sending only the minimal criteria needed for a match could identify many matches for each record you submit. To identify a "true match," you should provide as much of the information listed in Exhibit 1 in the NDI User's Guide as available.
The file years included in the search request are the years you identified on the Transmittal Form. Only those years will be searched for potential matches for your records.
Repeated searches
NDI staff must approve any request for repeated searches of NDI data. NDI staff will request your assurance that no significant changes have taken place since the initial application approval. Examples of significant changes are a new principal investigator, new funding source, or another party receiving identifiable data. If a significant change has occurred, then you must update your existing NDI application before a repeat search request will be approved.
If your project would like to request a repeated search, the project's principal investigator must send an email to ndi@cdc.gov for the application to be unlocked.
Find more detailed information about repeated use of NDI on page 4 of the application criteria document.
NDI Plus service
The NDI Plus service provides cause of death information at an additional cost to the researcher. These data are provided only for "true matches," not all matches. A true match is the one that is likely to be correct for a given subject.
Cause of death information is provided as permitted by the laws governing the jurisdiction of death.