# Presentation: 727874

## National Health Interview Survey (NHIS) Linked Mortality File Overview

**Christine S. Cox**
**Special Assistant for Record Linkage**

**Bryan Sayer, Donna Miller, Jim Brittain**

## National Health Interview Survey (NHIS)

- Nationally representative household based survey of the civilian non-institutionalized U.S. population.
- Conducted continously
- Surveys approximately 43,000 households per year for a total person sample of about 100,000
- Collects information on health conditions and utilization, access to care and health insurance coverage, along with other varying special topics of interest
- Survey design materials, questionnaires, and analytic reports available from the NCHS web site. http://www.cdc.gov/nchs/nhis.htm

## National Death Index 

- A centralized electronic data base containing death information from U.S. death certificates
- Available by application for statistical research only
- Users submit records containing study participant data to attempt to match to correct death record
- Each death record contains: demographic characteristics of the decedent, state of death, underlying/multiple causes of death
- Current Coverage:  1979-2002
- NDI webpage: http://www.cdc.gov/nchs/r&d/ndi/ndi.htm

## NHIS-NDI Linkage

- Conducting NDI data linkage is both a scientifically valuable and cost effective data collection activity.
- Provides the opportunity to conduct a wide variety of mortality outcome studies analyzing NHIS questionnaire data on  health conditions, insurance coverage, health behaviors and other risk factors
- Example:  breast cancer death rates among uninsured vs. insured women

## Previous vs. current NHIS Linked Mortality files

- Previous NHIS Mortality Data Files
- 1986-1994 NHIS Mortality Data through 1995
- 1986-1994 NHIS Mortality Data through 1997
- Current NHIS Linked Mortality File
- 1986-2000 NHIS Mortality Data through 2002

## NHIS – NDI Mortality Linkage Methodology

- Based on a probabilistic match to the NDI
- No death certificates were collected for  verification purposes
- Calibration study was conducted
- Best plausible NDI match record provided on user file (Definite non-matches eliminated)
- Final match status assigned
- Presumed Dead, Presumed Alive, Ineligible

## Ineligible Population

- All NHIS respondents under age 18 are not eligible for mortality follow-up
- All adult NHIS respondents who do not meet the minimum criteria set by NDI are defined as ineligible.
- SSN, sex, m/d/y of birth present
- Last name, first initial, month of birth, year of birth present
- Last name, first initial, SSN present
- Analysts should treat ineligibles as lost to follow-up
- New sample weights developed

## Percent of ineligible and deceased adult NHIS respondents by survey year : NHIS 1986-2000

## Total NHIS Deaths By Survey Year

| Survey Year | Total Number of Deaths |   | Survey Year | Total Number of Deaths |
| --- | --- | --- | --- | --- |
| 19861 |  8,492 |   | 1994 | 7,911 |
| 1987 | 15,776 |   | 1995 | 5,762 |
| 1988 | 14,695 |   | 19961 | 3,004 |
| 1989 | 12,956 |   | 1997 | 4,007 |
| 1990 | 12,061 |   | 1998 | 3,009 |
| 1991 | 11,014 |   | 1999 | 2,192 |
| 1992 | 10,596 |   | 2000 | 1,531 |
| 1993 |  8,130 |   | Total |          121,136 |

- 1 The 1986 and 1996 NHIS were fielded with a reduced sample.

## Cumulative survival curves, all males: NHIS 1987 and 1995 

## NHIS Linked Mortality File Access

- NCHS Research Data Center (RDC)
- Purpose –
- To provide access to restricted data files which data users would not be able to otherwise access
- Accessibility –
- On-site access – NCHS, Hyattsville, MD
- Off-site access - User’s remote location

## User Procedures

- To gain access to NCHS restricted data users must:
- Submit a research proposal	and receive approval
- Sign an affidavit of confidentiality and promise not to use any method to attempt to identify respondents
- Submit data files to be linked with RDC data ahead of time – _all_ linking is conducted by RDC staff
- Subject all output and/or materials removed from the RDC to a _disclosure limitation review_
- Pay a user’s fee that will be estimated prior to proposal approval

## RDC Contact Information

- For general Questions/Comments
- Email: rdca@cdc.gov      Phone: (301)458-4732
- For On-site Info: Negasi Beyene
- Email: NBeyene@cdc.gov    Phone: (301)458-4097
- For Remote Access Info: Vijay Gambhir
- Email: vgambhir@cdc.gov Phone: (301)458-4226

## File Structure

- A standard linked mortality file has been developed to assist RDC users:
- All variables on the standard will be linked to approved researcher’s analytic file (no need to specify variables of interest)
- Additional variables available by special approval only
- Geography
- Occupation & Industry

## Linked Mortality File Structure 

- Separate mortality data file for each NHIS survey year containing the total number of NHIS respondents for that survey year
- File documentation will be available for download on the NCHS Data Linkage web page (www.cdc.gov/nchs/rd.htm)
- Send email queries to (datalinkage@cdc.gov)
- Include NHIS Linked Mortality File in Subject line if possible for quicker routing

## Standard NHIS Linked Mortality File

- NHIS Public Use ID
- Eligibility Status
- NDI match results
- Date of Birth and Death (to calculate survival period)
- Underlying and Multiple Causes of Death
- Sample weights

## NHIS Survival period

- Decedents (Presumed Dead)
- End date = date of death
- Survivors (Presumed Alive)
- End date = December 31, 2002
- Some respondents appear to have very advanced ages (Dec. 31, 2002 – Date of birth)
- Analysts should consider reassigning these cases as lost-to-followup (otherwise immortal) or review the NDI results to see if a “close to match” NDI record exists that could be reassigned as deceased

## Cause of death codes Underlying cause of death recode groups

- ICD-9 (1986-1998)
- 282
- 72
- 34

- ICD-10 (1999-2002)
- 358 (all years coded)
- 113 (all years coded)
- 39