Description

The National Health Interview Survey (NHIS) is the principal source of information on the health of the civilian noninstitutionalized population of the United States and is one of the major data collection programs of the National Center for Health Statistics (NCHS). The National Health Survey Act of 1956 provided for a continuing survey and special studies to secure accurate and current statistical information on the amount, distribution, and effects of illness and disability in the United States and the services rendered for or because of such conditions. The survey referred to in the Act, now called the National Health Interview Survey, was initiated in July 1957. Since 1960, the survey has been conducted by NCHS, which was formed when the National Health Survey and the National Vital Statistics Division were combined.

NHIS data are used widely throughout the Department of Health and Human Services (DHHS) to monitor trends in illness and disability and to track progress toward achieving national health objectives. The data are also used by the public health research community for epidemiologic and policy analysis of such timely issues as characterizing those with various health problems, determining barriers to accessing and using appropriate health care, and evaluating Federal health programs.

The NHIS also has a central role in the ongoing integration of household surveys in DHHS. The designs of two major DHHS national household surveys are already linked to the NHIS, the National Survey of Family Growth and the Medical Expenditure Panel Survey. Other DHHS surveys will be linked to the NHIS in the future. These linked surveys will use the NHIS respondent sample as a sampling frame, will obtain additional information from their sample drawn from the NHIS, and will then combine that data with the information collected in the original NHIS interview.

While the NHIS has been conducted continuously since 1957, the content of the survey has been updated about every 10-15 years. In 1996 a substantially revised NHIS content began field testing. This new questionnaire, described in detail below, began in 1997 and improves the ability of the NHIS to provide important health information.

Purpose and Scope
The main objective of the NHIS is to monitor the health of the United States population through the collection and analysis of data on a broad range of health topics. A major strength of this survey lies in the ability to display these health characteristics by many demographic and socioeconomic characteristics.

The NHIS covers the civilian noninstitutionalized population of the United States living at the time of the interview.  Because of technical and logistical problems, several segments of the population are not included in the sample or in the estimates from the survey. Persons excluded are patients in long-term care facilities; persons on active duty with the Armed Forces (though their dependents are included); and U.S. nationals living in foreign countries.

Sample Design
The National Health Interview Survey is a cross-sectional household interview survey. Sampling and interviewing are continuous throughout each year. The sampling plan follows a multistage area probability design that permits the
representative sampling of households. The sampling plan was redesigned in 1995. Information about the sampling plan given here covers the design years of 1995-2004. The first stage consists of a sample of 358 primary sampling units (PSU's) drawn from approximately 1,900 geographically defined PSU's that cover the 50 States and the District of Columbia.  A PSU consists of a county, a small group of contiguous counties, or a metropolitan statistical area.

Within a PSU, two types of second-stage units are used: area segments and permit area segments. Area segments are defined geographically and contain an expected eight or twelve addresses. Permit area segments cover geographical areas containing housing units built after the 1990 census. The permit area segments are defined using updated lists of building permits issued in the PSU since 1990 and contain an expected four addresses. Within each segment all occupied households at the sample addresses are targeted for interview.

The NHIS sample design implemented with the 1995 data collection year was a complete redesign from that used during 1985-94. A feature added for the 1995 sample design is the oversampling of both Black persons and Hispanic persons. Another feature added is that the NHIS sample is now drawn from each State. Although the NHIS sample is too small to provide State level data with acceptable precision for each State, this design will facilitate the use of NHIS data with State-level telephone health surveys.

The total NHIS sample of PSU's is subdivided into four separate panels, or subdesigns, such that each panel is a representative sample of the U.S. population. This design feature has a number of advantages, including flexibility for the total sample size. The 1995 NHIS sample included all four panels. In the first half of 1996, the NHIS fielded the traditional pencil and paper NHIS questionnaire in 3 panels; in the second half of 1996 the NHIS fielded the traditional pencil and paper NHIS in 2 panels; most of the residual 1996 NHIS sample was used for the development of the revised NHIS questionnaire.

The households selected for interview each week in the NHIS are a probability sample representative of the target population. With four sample panels, NHIS data are collected annually from approximately 43,000 households including about 106,000 persons. Survey participation is voluntary and the confidentiality of responses is assured under Section 308(d) of the Public Health Service Act. The annual response rate of NHIS is greater than 90 percent of the eligible households in the sample.

Content of the Questionnaire
The NHIS that was fielded from 1982-1996 consisted of two parts: (1) a set of basic health and demographic items (known as the Core questionnaire), and (2) one or more sets of questions on current health topics. The Core questionnaire remained the same over that time period while the current health topics changed depending on data needs. The NHIS Core, while collecting useful data on health conditions and utilization, did not collect any information on insurance, access to health care, or health behaviors. In addition, much of the interview time in the Core was devoted to collecting detailed information on events such as doctor visits and hospitalizations rather than on information that would better characterize the individual. The revision of the NHIS has attempted to address these and other shortcomings.

The revised NHIS will have three parts or modules: a Basic module; a Periodic module; and a Topical module. The Basic module will function as the new Core questionnaire. It will remain largely unchanged from year to year and will allow for trends analysis and for data from more than one year to be pooled to increase sample size for analytic purposes. The Basic Module contains three components: the Family Core, the Sample Adult Core, and the Sample Child Core. The Family Core component will collect information on everyone in the family and will also allow the NHIS to serve as a sampling frame for additional integrated surveys as needed. Information to be collected on the Family Core for all family members includes: household composition and sociodemographic characteristics; tracking information; information for matches to administrative data bases; and basic indicators of health status and utilization of health care services.

From each family in the NHIS, one sample adult and one sample child, if any, will be randomly selected and information on each will be collected with the Sample Adult Core and the Sample Child Core questionnaires. Because some health issues are different for children and adults, these two questionnaires differ in some items but both will collect basic information on health status, health care services, and behavior. The Basic module was fielded in 1997.

The content and timing of the Periodic module has not yet been determined, and will depend in part on experience gained in fielding the Basic module. The purpose of the Periodic module is to collect more detailed information on some of the topics included in the Basic module from the sample persons. This will provide greater depth in certain areas while retaining key measures in all areas for cross analysis.

The Topical module is analogous to the supplement section of the current NHIS and will be used to respond to new public health data needs as they arise. As with current NHIS supplements, the questionnaires in the Topical module may be fielded only once or may be repeated as needed. These questionnaires may be used to provide additional detail on a subject already covered in the Basic or Periodic modules or on a different topic not covered in other parts of the NHIS. The first Topical module will be fielded in 1998 and will focus on data needed to track the Year 2000 health objectives.

Data Collection Procedures
Data are collected through a personal household interview conducted by interviewers employed and trained by the U.S. Bureau of the Census according to procedures specified by   NCHS.

For the Family Core component of the Basic module, 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. For children and for adults not at home during the interview, information is provided by a responsible adult family member (18 years of age and over) residing in the household. For the Sample Adult questionnaire, one adult per family will be randomly selected; this individual must respond for themselves to the questions in this section. Information for the Sample Child questionnaire will be obtained from a knowledgeable adult in the household.

The Bureau of the Census under a contractual agreement is the data collection agent for the NHIS. Nationally, the NHIS uses about 400 interviewers, trained and directed by health survey supervisors in each of the 12 Bureau of the Census Regional Offices. The supervisors are career Civil Service employees whose primary responsibility is the National Health Interview Survey. The interviewers are part-time employees, selected through an examination and testing process. Interviewers receive thorough training in basic interviewing procedures and in the concepts and procedures unique to the NHIS.

In the past the NHIS interview have been conducted using paper and pencil. The revised NHIS questionnaire is conducted using a computer assisted personal interviewer (CAPI). The CAPI version of the NHIS questionnaire is administered using a laptop computer and interviewers enter responses directly into the computer during the interview. This computerized mode offers distinct advantages in terms of timeliness of the data and improved data quality.

For publications and information:
Data Dissemination Branch
National Center for Health Statistics
Centers for Disease Control and Prevention
3311 Toledo Road, Room 5407
Hyattsville, Maryland 20782-2003
(301) 458-4636
Internet home page address:
www.cdc.gov/nchs/

For program assistance:
Division of Health Interview Statistics
National Center for Health Statistics
Centers for Disease Control and Prevention
3311 Toledo Road, Room 2217
Hyattsville, Maryland 20782-2003
(301) 458-4901