The National Health Interview Survey (NHIS) is the principal source of information on the health of the civilian noninstitutionalized population of the United States. The NHIS 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 U.S. 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.
The objective of the survey is to address major current health issues through the collection and analysis of data on the civilian noninstitutionalized population of the U.S. National data on the incidence of acute illness and injuries, the prevalence of chronic conditions and impairments, the extent of disability, the utilization of health care services, and other health-related topics are provided by the survey. A major strength of this survey lies in the ability to display these health characteristics by many demographic and socioeconomic characteristics.
The NHIS data are obtained through personal interviews with household members. Interviews are conducted each week throughout the year in a probability sample of households. The interviewing is performed by a permanent staff of interviewers employed by the U.S. Bureau of the Census. Data collected over the period of a year form the basis for the development of annual estimates of the health characteristics of the population and for the analysis of trends in those characteristics.
The survey covers the civilian noninstitutionalized population of the U.S. 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 int 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.
The NHIS is a cross-sectional household interview survey. Sampling and interviewing are continuous through each year. The sampling plan follows a multistage area probability design that permits the representative sampling of households. The first stage consists of a sample of about 200 primary sampling units (PSUs) drawn from approximately 1,900 geographically defined PSUs 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 PSUs, intermediate stage units called segments are defined in such a manner that each segment contains approximately 40 households. Within these segments, a systematic sample of eight households is selected for the NHIS sample.
The NHIS sample implemented with the 1985 data collection year was a complete redesign from previous years. A feature that was added for the 1985 design is the formation of panels of PSUs. The total NHIS sample of PSUs is subdivided into four separate panels 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 1985 NHIS sample included three out of the four panels and the 1986 NHIS sample includes two panels.
Another design feature implemented in 1985 is the over-sampling of black persons to improve the precision of estimates for that population. This resulted in an increase in the number of black persons in the NHIS sample by approximately 75 percent and an increase in the precision of most related statistics by more than 20 percent. The new sample design also facilitates followup studies of respondents and linkage with other national health-related data sets such as the National Death Index.
The households selected for interview each week are a probability sample representative of the target population. With four sample panels, data are collected from approximately 50,000 households including about 135,000 persons in a calendar year. Participation is voluntary and confidentiality of responses is guaranteed. The annual response rate of NHIS is over 95 percent of the eligible households in the sample. The response is divided equally between refusals and households where no eligible respondent could be found at home after repeated calls.
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.
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 (19 years of age and over) residing in the household. Between 65 and 70 percent of the adults 17 years of age and over are self-respondents. Generally, a random subsample of adult household members is selected to respond for themselves to questions on current health topics that are added each year.
Nationally, there are approximately 150 interviewers, trained and directed by health survey supervisors in each of the 12 Census Bureau Regional Offices. The supervisors are career Civil Service employees whose primary responsibility is the NHIS. 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.
Depending on the family size and the nature and extent of health conditions of family members, the length of interview ranges 20-90 minutes. On the average, the interviews require about 50 minutes in the household.
The questionnaire consists of two basic parts: (1) a set of basic health and demographic items, and (2) one or more sets of questions on current health topics. The basic items constitute approximately 50 percent of the questionnaire and are repeated each year. These items provide continuous information on basic health variables. Questions on current health topics facilitate a response to changing needs for data and coverage of a wide variety of issues. This combination yields a unique national health data base.
The questionnaire includes the following types of basic health and demographic questions:
Demographic characteristics of household members, including age, sex, race, education, and family income.
Disability days, including restricted-activity and bed-disability days, and work- and school-loss days occurring during the two-week period prior to the week of interview, as well as 12-month bed days.
Physician visits occurring during the same two-week period, interval since the last physician visit, and the number of visits in the last 12 months.
Acute and chronic conditions responsible for these days and visits.
Long-term limitation of activity resulting from chronic disease or impairment and the chronic conditions associated with the disability.
Short-stay hospitalization data, including the number of hospital episodes during the past year and the number of days for each stay.
In addition, each of six representative subsamples is asked to respond to questions about one of six lists of selected chronic conditions.
Questions on special health topics change in response to current interest and need for data. The 1983 questionnaire contained questions on alcohol, dental care, physician services, and health insurance. The 1984 current health topic questionnaire was devoted entirely to issues of aging, 1985 covered health promotion and disease prevention, and 1986 includes questions on health insurance, dental health, vitamin and mineral intake, longest job worked, and functional limitations. The 1987 NHIS includes an extensive questionnaire on cancer risk factors and questions on child adoption.
Suggestions and requests for special health topics are solicited and received from many sources. These include university-based researchers, administrators of national organizations and programs in the private and public health sectors, and other parts of the U.S. Department of Health and Human Services such as the National Institutes of Health and the Centers for Disease Control. Topics are selected after consultation with agencies within the Public Health Service and after an assessment of priority health issues and the related need for population-based data. A lead time of at least 18 months is required to develop and pretest questions for new topics.
The objective of the National Health Interview Survey (NHIS) is to address major current health issues through the collection and analysis of data on the civilian noninstitutionalized population of the United States.
The NHIS questionnaire consists of two basic parts: (1) a set of basic health and demographic items, and (2) one or more sets of questions on current health topics. The basic items constitute approximately 50 percent of the questionnaire and are repeated each year. This provides continuous national data on basic health topics and permits assissment of trends and changes in the health status and health-related characteristics of the population. The current health topics questionnaire generally changes each year. this facilitates a response to the need for population-based data on current or emerging health issues and coverage of a wide variety of topics. This combination yields a unique national health data base.
The basic health and demographic questionnaire includes the following items:
Demographics
Health Status
Health Care Utilization
Extensive information is obtained about each condition, each hospital stay in the past 12 months, and each doctor visit in the past two months.
Suggestions and requests for special health topics are solicited and received from many sources. These include university-based researchers, administrators of national organizations and programs in the private and public sectors, and other parts of the U.S. Department of Health and Human Services such as the National Institutes of Health and the Centers for Disease Control. Topics are selected after consultation with agencies within the Public Health Service and after an assessment of priority health issues and the related need for population-based data. A lead time of at least 18 months is required to develop and pretest questions for new topics.
Current health topics covered by the NHIS include:
1987
* On both Cancer Risk Factor Questionnaires
1986
1985
1984
1983
1982
1981
1980
1979
1978
1977
1976
1975
1974
1973
1972
1971
1970
1969
Further information about the NHIS questionnairs can be obtained from the Division of Health Interview Statistics.
Data tapes on NHIS current health topics, such as the 1985 survey on health promotion and disease prevention, can be purchased directly from the Division of Health Interview Statistics.
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
* Price for tape at 1600 BPI is $275.
** Available December 1986.
These data tapes are available for purchase from the Division of Health Interview Statistics, National Center for Health Statistics, 3700 East-West Highway, Hyattsville, MD 20782. The order form is on the reverse side. Additional information is available upon request.
| ORDER FORM | |
| Data Purchase and Use Agreement. Individual identifiers have been removed from the microdata public use tapes available from the National Center for Health Statistics. Nevertheless, section 308(d) of the Public Health Service Act (42 U.S.C. 242m) specifies that data collected by the National Center for Health Statistics may not be used for any purpose other than that for which is was supplied. The information on the microdata public use tapes available for purchase was supplied to NCHS for statistical research and reporting purposes. It is necessary, therefore, that the individual ordering such tapes sign the following assurance: | |
| The undersigned gives assurance that individual elementary unit data on the microdata public use tapes being ordered will be used solely for statistical research or reporting purposes. | |
| SIGNED: | DATE: |
| TITLE: | ORGANIZATION: |
| DATA TAPES ORDERED: | |
| - | |
| - | |
| - | |
| PROPOSED USE: | |
| - | |
| - | |
| This form may be used for ordering data sets. Indicate the data sets you want, put your name and address below, enclose payment, and sent to: Division of Health Interview Statistics, National Center for Health Statistics, Center Building, Room 2-44, 3700 East-West Highway, Hyattsville, Maryland 20782, (301)436-7087. Make check payable to: U.S. Department of Health and Human Services (for Statistical Studies). | |
| SEND INDICATED DATA SETS TO: | |
| - | |
| - | |
| - | |
| - | |
Concerns among a number of public health agencies and individuals about the increasing proportion of older people in the United States population led, as early as 1980, to recommendations that the National Health Interview Survey (NHIS) address this special subgroup. Issues dealing with the health and functional status of older people and the need for alternatives to institutionalization as the mode for providing care were identified at this early point by professionals in the field of aging. Information about these and related characteristics of the older population was needed.
Statements of the need for this information were made by the Department of Health and Human Services in the 1980 National Long Term Care Plan of the Division of Long Term Care Policy, Office of the Assistant Secretary for Planning and Evaluation; by the Office of Management and Budget (OMB) in its 1980 report of the Interagency Statistical Committee on Long Term Care of the Elderly; and by the 1981 White House Conference on Aging.
It was postulated that information about the health conditions that were most prevalent, about living arrangements, family and social support availability, retirement income and financial obligations, functional status and limitations, and attitudes and opinions about their own health and abilities would help in assessing the future needs of the elderly.
In addition to responding to the topic recommendation of the NHIS's Technical Consultants Panel that these informational needs about the elderly could be addressed through the NHIS, a special Supplement on Aging (SOA) in 1984 was particularly timely because the National Center for Health Statistics (NCHS) planned to conduct the National Nursing Home Survey (NNHS) in 1984 (later postponed to 1985). An NHIS survey on the elderly would provide data on the noninstitutionalized population which would complement the NNHS data on residents of nursing homes and would provide, for the first time, comprehensive data on almost the total elderly population.
The development of a supplement to help provide some of this information from a national survey of elderly people themselves began in 1982 and resulted in the 1984 NHIS SOA. The SOA was sponsored and funded by NCHS, which was responsible for survey design, data processing, and preliminary analysis. Data collection was conducted by the Bureau of the Census under an interagency agreement.
The first step in development was to determine the topics to be included. Topic suggestions were received from a variety of sources inside and outside NCHS. Suggestions from outside NCHS came in response to the topic solicitation from the Division of Health Interview Statistics and from notification to interested agencies and persons, including the National Institute on Aging, the Administration on Aging, the U.S. Senate Select Committee on Aging, the Social Security Administration, voluntary and nonprofit organizations, and experts in the field of aging.
Selection of topics from those suggested was guided by three considerations: feasibility of collecting the data in a household interview survey; comparability to data collected in other NCHS surveys, especially the planned NNHS; and the creation of a baseline data source for a longitudinal study of aging. Activities undertaken in the topic selection process included literature reviews, reviews of earlier surveys, consultation with other agencies and individuals, and participation in conferences on the aging.
During this process it was decided that the information being sought would usually be most reliably reported by the sample person himself or herself; therefore, a rule was established that the sample person would respond for himself or herself except in cases where the sample person was physically or mentally unable to respond. In these cases, an adult, preferably living in the household, would be accepted as proxy.
The end result of this process was a pretest version of a questionnaire. Two pretests were conducted in the development of the SOA. Approval of OMB was requested in two submissions, the first covering the first pretest, and the second covering the second pretest and the full 1984 SOA. The first pretest (n=256) was conducted in June 1983 in Bradenton, Florida, which was selected because it is a popular location for retirement. The questionnaire was revised extensively on the basis of the Bradenton experience, and a second pretest was conducted in September 1983 in Wilmington, Delaware (n=234); subsequently, further revisions were made, resulting in the final form of the SOA questionnaire.
The NHIS sample is designed to produce national estimates for the civilian noninstitutionalized population residing in the United States. The United States is first divided into geographically defined primary sampling units, which cover the 50 states and the District of Columbia. These units are grouped in strata with similar characteristics, and in 1984 one unit was selected from each stratum. Within each selected unit, compact clusters of housing units are then selected for the sample. Because the sample is clustered, it is not a "simple random sample."
In 1984, 41,471 eligible households were in the NHIS sample, and interviews were conducted in 39,996 (96.4 percent), including 105,290 persons of all ages residing in the households at the time of interview. Details of the sample design for the 1984 NHIS are published in Vital and Health Statistics, Series 1, No. 18 and Series 10, No. 156.
Because the SOA intended to obtain information on both those who were currently elderly (over age 65), and to provide baseline information for longitudinal studies of persons who would become elderly in the next ten years, it was decided to include persons 55 years of age and older. However, because there are large numbers of persons 55-64, it was not necessary to include all NHIS sample persons in that age range to achieve the desired level of statistical precision. Therefore, the sample for the SOA consisted of all NHIS sample persons 65 years of age and over, and a systematic sample of 50 percent of NHIS sample persons 55-64 years of age.
A total of 16,347 persons were selected for the SOA, for whom 16,148 interviews were completed, for a 96.7 percent response rate; in more than 90 percent of the completed interviews the sample person was the respondent. The effective overall response rate for the NHIS-SOA (the product of the response rate on the NHIS and the SOA) was 93.2 percent.
The NHIS is designed to make national estimates of statistics; therefore, the data must be weighted to inflate the sample numbers to national estimates. The weights indicate the estimated number of persons in the population represented by each sample person, and depend (most importantly) on the probability of selection, the response rate in the sample segment, and an adjustment to independent estimates (from the Current Population Survey) of 60 age-sex-race population groups. In addition to these NHIS adjustments, the SOA had additional adjustments for nonresponse on the SOA and for the 50 percent subsampling rate for persons 55-64 years of age. These weights are included on the public use sample tapes, and should be used in estimating population statistics from the sample.
Because the SOA sample is large and its design is efficient, its estimates of population statistics are generally very precise. Vital and Health Statistics, Series 10, No. 156 includes instructions and examples for estimating sampling errors for estimates from the 1984 NHIS. Those procedures may be applied directly to estimates from the SOA for persons 65 and over; for persons 55-64, an additional step is necessary to account for the 50 percent subsample-multiplying variance estimates by 1.4. On average, the precision of estimates from the SOA is nearly as good as from a simple random sample of the same size: standard errors of estimates from the SOA would average less than 25 percent greater than from a single random sample of the same size.
Data were collected in personal interviews. Almost always the respondent was the sample person, and almost always the interviews were face-to-face; however, proxy respondents and telephone interviews were permitted in certain circumstances when necessary to complete interviews.
Interviewing for the 1984 SOA was conducted by the Bureau of the Census, Field Division, in the standard face-to-face interviewing procedure for conducting the NHIS. The interviews period for the 1984 NHIS and SOA was January 9, 1984 through January 6, 1985, with interviewing conducted weekly throughout the year.
NHIS interviewer training is conducted by the Bureau of the Census and consists of two types: initial training for new NHIS interviewers; and annual training for experienced interviewers on the current year's special procedures and special topics questionnaires. The initial training for NHIS interviewers takes about a full week and includes about one and one-half days for any supplement to be covered; this was modified to give additional time for training new interviewers on the SOA. Training on the SOA for experienced interviewers consisted of one and one-half days of classroom sessions in January, and portions of a later one day training session and five hours of home study materials.
A number of measures are taken in the NHIS to control the quality of data collection. All inter- viewers are observed in the field by supervisory personnel at least twice each year, with new interviewers and interviewers with problems being observed more frequently. Interviewers are required to edit all completed interview schedules before submitting them to their supervisors in the Census Regional Offices, where additional edits are done; this editing is more intensive in the early part of a data collection year and for new interviewers. Approximately 5 percent of all interviews are designated for re-interview. The re-interview serves as a check on interviewer performance and as a measure of the reliability and accuracy of the NHIS and SOA data. For each household designated for re-interview, a subset of questions is asked by telephone by the interviewing supervisor.
Quality control measures also are taken during the processing of data by NCHS staff. Quality control of the coding of questionnaire information consists of recoding 10 percent of all questionnaires by two independent coders. The quality of machine keying is maintained by a 100 percent independent key verification of all items in the questionnaires. After the data are on tape, computer edits are performed in the preparation of final data tapes. The computer edit checks for inconsistencies and invalid responses, provides algorithms for imputation, and generates recodes. The specifications for computer edits for the SOA included more than 350 decision logic tables.
The SOA data tapes are in EBCDIC format and contain the SOA interview information with the following record structure: (1) a file of person records containing, for each person for whom an interview was completed, all items in the NHIS basic questionnaire that are on the person file, weights, all items in the SOA questionnaire (except the items used to permit matching to the National Death Index), special recodes, and selected condition and utilization information; and (2) a file of condition records, containing all conditions mentioned in the SOA interview plus any condition for the individual that is related to a "limited activities" status from the basic NHIS questions. To protect confidentiality, no items are included on the data tape which would uniquely identify an individual respondent. The detail of the content, coding, and structures of these two SOA data record types is contained in the public use tape documentation.
For the person tape DSN=HISY1984.AGINGPER, LRECL=1001, BLKSIZE=31031, and COUNT=16148. For the condition tape, DSN=HISY1984.AGINGCON, LRECL=380, BLKSIZE=31920 and COUNT=46320. Both tapes are standard label and are available in either 1600 BPI or 6250 BPI.
Preliminary reports based on data collected in the first six months of 1984 have been published in the NCHS series ADVANCE DATA, Numbers 115, 116, 121, 124, and 125. They focus on demographic and general health measures (115), persons living alone (116), urinary problems (121), community services (124), and vision and hearing impairments (125). Comparable analyses on the same topics were done using data for the full 12 months and presented in a special session at the 1986 meetings of the Gerontological Society of America. Additional ADVANCE DATA reports, based on the full year of data, which are soon to be published focus on functional limitations (activities of daily living and instrumental activities of daily living), and on ability to perform work related activities. A detailed analysis of the SOA data on functional limitations is in preparation for publication in Vital and Health Statistics, Series 10; and a full report on the SOA methodology entitled "The Supplement on Aging to the 1984 National Health Interview Survey," authored by Joseph E. Fitti and Mary Grace Kovar, will soon be published in Vital and Health Statistics, Series 1, No. 21. Additional analyses by staff of NCHS and other Federal agencies on a variety of topics are underway or planned. More than 30 public use data tapes have been sold by NCHS to researchers in universities and research centers, and the National Institute on Aging is encouraging applications for grants to conduct research using the SOA data.
Public use data tapes from the SOA may be purchased form NCHS for $275, which includes two data tapes (described above) and all documentation. Orders should be mailed to the Division of Health Interview Statistics, National Center for Health Statistics, Center Building, Room 2-44, 3700 East-West Highway, Hyattsville, Maryland 20782, with a check made payable to the U.S. Department of Health and Human Services for Statistical Studies. The order should include an assurance that the data will be used solely for statistical research or reporting purposes. The density desired, 1600 BPI or 6250 BPI, should be specified. Order forms are also available from the same address.
Reproduced for the conference package from the NCHS Health Interview Statistics newsletter. Copies can be obtained from U.S. Public Health Service, National Center for Health Statistics, Division of Health Interview Statistics, Room 2-44, 3700 East-West Highway, Hyattsville, MD 20782, (301)436-7085.
Excerpted or abstracted from Joseph E. Fitti and Mary Grace Kovar, "The Supplement on Aging to the 1984 National Health Interview Survey," Vital and Health Statistics, Series 1, No. 21, DHHS Publication No. (PHS)87-1323 (in preparation). Available from the U.S. Government Printing Office Beginning Summer, 1987