Using Linked Data Products

If you are interested in using the NCHS linked data products, we recommend that you carefully review the data documentation available on this website. The documentation will help answer the questions:

1. Which NCHS surveys (e.g., NHANES, NHIS, or NNHS) were linked to administrative records?
2. What years of the NCHS survey and administrative records were linked?
3. What variables are available from the administrative records?

For information about survey design, questionnaire, and variables for applicable surveys, please refer to the Surveys and Data Collection Systems webpage.

Please select the linked data product on the navigation menu for more information.

Description of feasibility files

NCHS has created and released for public use feasibility files for most of its linked data products. These files provide information about survey respondents’ eligibility for data linkage and final match status for survey respondents. These files can be used to determine the maximum available sample size to assess the feasibility of conducting analyses using the linked data. For the restricted-use linked mortality data, the public-use linked mortality file can be used as a feasibility file.

When merged with public-use data from linked NCHS surveys, feasibility files make it possible to:

• identify demographic and health status variables available in the public-use survey that may be of interest in subdividing the survey sample
• calculate estimates of numbers of individuals in categories of interest
• determine cell sizes by related categories
• determine if there are sufficient numbers of individuals in the category of interest who have been successfully linked to administrative data to answer your specific research question

It is important to note that the feasibility files do not contain any specific information about survey respondents’ linked administrative records.

Download the feasibility files and merge with public-use data from NCHS surveys

1. Go to the specific data linkage website and click the link for feasibility files.
2. Download the file(s) to your computer.
3. Use the sample SAS or Stata programs to read the feasibility files into SAS or Stata.
4. Create an extract using NCHS public-use survey data. Visit the appropriate survey website for instructions on how to create an extract using NCHS public-use survey data.
5. Merge public-use data from the extract using NCHS public-use survey data with the feasibility file, using the public-use identifier (e.g., PUBLICID for NHIS, SEQN for NHANES).

With the exception of the public-use linked mortality files, NCHS linked files are restricted for research use and the data are only accessible through the NCHS Research Data Center (RDC), a secure data access portal. Federal law requires NCHS to safeguard confidential information. RDC is responsible for protecting the confidentiality of survey respondents, study subjects, or institutions from which data were collected.

To work with these data files, you must submit a proposal to the RDC. For information about the RDC proposal process, visit the RDC website.

Contact the datalinkage@cdc.gov for questions about the linked data products.