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The NHIS is sponsored by the National Center for Health Statistics (NCHS), which also sponsored the National Health Interview Survey on Disability (NHIS-D) conducted in 1994-1997. Data were collected by employees of the U.S. Bureau of the Census, using procedures developed by the NCHS. The NHIS is designed to monitor the health of the United States population through a survey of a broad range of health topics.
The survey is a nationally representative sample of the resident civilian, non-institutionalized U.S. population, both children and adults. It does not include residents of long-term care facilities, persons on active duty with the Armed Forces (though their dependents are included); or U.S. nationals living in foreign countries.
The NHIS has been conducted annually since 1957. Sampling and interviewing are done continuously throughout the year.
Data are collected through an in-person household interview conducted by interviewers employed by the U.S. Bureau of the Census. Since 1997, the NHIS has been administered using computer assisted personal interview (CAPI), in which interviewers enter responses onto a laptop computer during the interview.
The NHIS includes a core questionnaire that has three components: a Family Core, which collects information on everyone in the family living in the household; a Sample Adult Core, which collects information on a randomly selected adult in the household; and a Sample Child Core, which collects information on a randomly selected child.
For the Family Core, all adult members of the household 17 years of age and over who are at home at the time of the interview are invited to participate and to respond for themselves. A responsible adult family member age 18 or over who resides in the household provides information for children and for adults not at home at the time of the interview.
The NHIS uses a complex stratified sampling strategy that has changed over time. The current 1995-2004 NHIS identifies 358 geographic sampling areas and then selects groups of addresses within each area. Occupants at all the sample addresses are asked to participate in interviews.
For data collected in 1995 through 2004, the survey was designed to yield an annual sample of 44,000 occupied households with data on 106,000 individuals. The actual sample size has varied over the years between 36,000 to 47,000 households, and between 92,000 to 125,000 individuals. Since 1995 the survey has oversampled the Black and Hispanic populations to improve statistical precision.
The content of the survey has evolved over time. NHIS underwent a major revision in 1997. The redesigned questionnaire includes three components: the Family Core, the Sample Adult Core, and the Sample Child Core.
The Family Core addresses the topics of:
The Sample Adult Core covers:
The Sample Child Core addresses:
Supplementary questions. The Core questionnaires may also include supplementary questions merged into the regular core questions or placed at the end of a section of a core questionnaire. For example the 2001 Sample Child Core included a set of questions about child mental disorders and symptoms; the 2001 Sample Adult Core included questions about social support. (These supplementary questions have also been referred to as "topical modules" or "periodic modules.")
The NHIS defines disability in terms of limitations in a person's activity due to a health condition or impairment. Activity limitation is defined in terms of age-appropriate activities such as playing, participating in Special Education, or working.
For each adult age 18 and over, NHIS asks if the person
For children under 5, the NHIS asks if the child:
For 5- to 17-year olds, the NHIS asks the same set of questions asked of younger children, with the exception of the question about play.
Because of the small sample size, the NHIS cannot provide reliable state-level estimates. There are additional problems imposed by questionnaire content and design. The 1997 re-design of the activity limitation section may have resulted in better identification of children and elderly people with disabilities, but significant numbers of working-age adults are no longer identified due to procedural and wording changes.
Functional limitation questions have been added to the NHIS to supplement its questions on limitations in major activities. Tabulation of these questions has resulted in inflation of the purported size of the disability population, without any analysis of whether the reported difficulties significantly affect respondents' lives.
The NHIS home page at http://www.cdc.gov/nchs/nhis.htm includes links to the major NHIS publications, downloadable data sets, documentation, and questionnaires. Those of particular interest to disability researchers include:
Series 10 reports (http://www.cdc.gov/nchs/products/pubs/pubd/series/sr10/ser10.htm) include annual basic survey estimates for various population subgroups, including those defined by age, gender, race, family income, and other variables. Separate reports are issue for the U.S. population, the adult population, and children.
Public Use Data Sets are microdata files that are released annually. These are downloadable from the NHIS Web site, and are also available on CD-ROM (for years 1987-97) and on tape (for years 1969-96). from the NHIS Web site as well as on CD-ROM.
Design and estimation for the National health Interview Survey, 1995-2004 (Series 2, No. 130), part of "Data Evaluation and Methods Research" series (series 2), provides an overview of the NHIS sample design and data analysis methods.
For publications and further information: Data Dissemination Branch
National Center for Health Statistics
Centers for Disease Control and Prevention
3311 Toledo Road, Room 5407
Hyattsville, Maryland 20782-2003