Frequently Asked Questions

1. What surveys have been linked to which administrative/follow-up data?

The following table presents the NCHS surveys and the administrative data source(s) each is linked to:

• Data Linkage Resources by NCHS Health Surveys [PDF – 100 KB]

 

2. Where can I find a list of variables from the different restricted-use linked data files to construct my data dictionary for my RDC proposal?

• Linked Mortality Files:
  • Restricted Use Data Dictionary: Restricted-Use 2011 Linked Mortality File [PDF – 176 KB]
  • Public-Use Data Dictionary: Public-Use 2011 LMF Data Dictionary [PDF – 390 KB]
• Linked Centers for Medicare and Medicaid Services (CMS) Files:
  • Medicare - Variable List [PDF – 290 KB]
  • Medicaid – Variable List [PDF – 403 KB]
• End-Stage Renal Disease (ESRD) Data: Variable List [PDF – 291 KB]
• Linked Social Security Administration (SSA) Files: Data Dictionary [PDF – 1.84 MB]
• Linked Housing and Urban Development (HUD) Files: Data Dictionary [PDF – 1.02 MB]

 

3. Can files be linked across the different administrative data sources?

Yes, an analyst can request access to multiple linked data files across the different administrative data sources. For example, an analyst may be interested in Medicare claims data as well as mortality outcomes for NHANES III survey respondents.  This analyst would request access to both the NHANES III linked Medicare files and NHANES III linked Mortality File in their RDC proposal.

 

4. I am interested in pooling multiple years of NHIS.  Are there any special issues I should be aware of?

Yes. There are people in the 1991 NHIS sample who are also in the 1992 NHIS sample.  If you are combining those two years, you need to use the special 1992 NHIS file that excludes the people who were also interviewed in 1991.  The NHIS website has more information on how to select these individuals. The NHIS has also undergone survey design changes over the years that researchers may need to address when pooling across NHIS years.  The NHIS website advises researchers on how to control for changes in the NHIS survey design.

 

5. Can I use previous releases of the linked mortality files?

The updated 2011 Linked Mortality Files supersede any previous data releases of mortality follow-up.  Improvements to the matching algorithm and personal identifier information make the latest mortality release more accurate than previous releases.  Therefore, we do not allow analysts access to previous releases of the restricted-use linked mortality files.  We do not recommend using outdated versions of public-use files.  Researchers will be allowed to finish work done on a prior release of the linked files as necessary and by a case by case basis.

 

6. What variables are used to merge the linked files with the individual surveys?

The variable to use to merge linked files with individual surveys varies by survey. The table below presents the merge keys.

NCHS Survey	Survey Participant Identification Variable
National Health and Nutrition Examination Survey (NHANES)	SEQN
Third National Health and Nutrition Examination Survey (NHANES III)	SEQN
Second National Health and Nutrition Examination Survey (NHANES III)	SEQN
NHANES Epidemiologic Follow-Up Study (NHEFS)	SEQN
National Health Interview Survey (NHIS)	PUBLICID*
Second Longitudinal Study on Aging (LSOA II)	PUBLICID*
National Nursing Home Survey (NNHS)	RESNUM**

* PUBLICID must be created by the user for NHIS and LSOA II

** RESNUM is the merge key for the 2004 NNHS.  FACID is the merge key for the 1997 NNHS and CRID is the merge key for the 1995 NNHS. 

7. How do I create PUBLICID?

PUBLICID is a function of several component variables and varies by year in NHIS. Please refer to the appropriate documentation, e.g. Appendix 2 of the Public-Use Linked Mortality File Data Dictionary [PDF – 390 KB].