NHIS Linked Mortality File 2019 Public-Use Data
About
The NHIS Linked Mortality File (LMF) provides users with information from the National Death Index (NDI) for eligible NHIS respondents. The National Center for Health Statistics (NCHS) website provides the following description of the NDI:
The National Death Index (NDI) is a central computerized index of death record information on file in the State vital statistics offices. Working with these State offices, NCHS established the NDI as a resource to aid epidemiologists and other health and medical investigators with their mortality ascertainment activities. [The NDI is] [a]vailable to investigators solely for statistical purposes in medical and health research.
The NCHS has assisted researchers by linking the records for NHIS survey participants with the NDI. The mortality variables in the NHIS public use files (and in IPUMS NHIS) are based on results from matches between NHIS records and NDI death certificate records. The NCHS website explains:
Linkage of the NHIS survey participants with the NDI provides the opportunity to conduct studies designed to investigate the association of a variety of health factors with mortality, using the richness of the NHIS questionnaires.
Available Data
To preserve the privacy of NHIS respondents, the NCHS restricts access to the full LMF data to their Research Data Center (RDC). To increase public access, the NCHS has developed a limited set of variables that include only adult participants. In addition, these data have been subjected to some perturbation techniques to reduce potential disclosure risk, and some synthetic data have been substituted for underlying cause of death for select records. Data on vital status have not been perturbed. The Public-use Linked Mortality File Readme from the NCHS offers details about how the public-use data were compiled. Complete information on how to submit a proposal to use the restricted LMF is available at the NCHS RDC website. IPUMS NHIS offers guidance for using harmonized IPUMS data with the restricted-use NHIS files in the FSRDC on our website.
2019 Release
The 2019 public-use LMF update includes linked mortality information for NHIS sample years 1986-2018. From 1986-2014, data exist for all eligible adult respondents, and from 2015-2018 for all eligible sample adults. Respondents are considered eligible for if they have provided sufficient identifying information for NCHS to link them accurately to the NDI. For detailed information about the linking methodologies NCHS uses, as well as analytic considerations for using LMF data, see The Linkage of National Center for Health Statistics Survey Data to the National Death Index – 2019 Linked Mortality File (LMF): Linkage Methodology and Analytic Considerations. Because not all NHIS survey respondents are eligible for linkage, special weights (MORTWT and MORTWTSA) are provided for use in mortality analysis. Please see the variable descriptions for these weights for usage guidance.
Prior LMF updates have included some variables that are not available in the current release. The mortality variables page lists all the mortality variables available in the IPUMS NHIS.
Other Resources
Other documents that may be of interest to researchers using LMF data are below:
- The National Vital Statistics System (NVSS) Public Use Data Documentation on Mortality Multiple Cause-of-Death
- The NVSS Report on the Comparability of Cause of Death Between ICD-9 and ICD-10
- Information on the restricted-use LMF Underlying and Multiple Cause of Death Codes
- Most of the linking of the NDI with the NHIS is done using deterministic methods, but some records use a probabilistic methodology based on A Theory for Record Linkage by Ivan P. Fellegi and Alan B. Sunter
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