About the National Health Interview Survey
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) which is part of the Centers for Disease Control and Prevention (CDC). 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.
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 categorize these health characteristics by many demographic and socioeconomic characteristics.
NHIS data are used widely throughout the Department of Health and Human Services (HHS) 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.
While the NHIS has been conducted continuously since 1957, the content of the survey has been updated about every 15-20 years to incorporate advances in survey methodology and coverage of health topics. In January 2019, NHIS launched a redesigned content and structure that differs from its previous questionnaire design (1997–2018).
NHIS is a cross-sectional household interview survey. The target population for the NHIS is the civilian noninstitutionalized population residing within the 50 states and the District of Columbia at the time of the interview. The NHIS universe includes residents of households and noninstitutional group quarters (e.g., homeless shelters, rooming houses, and group homes). Persons residing temporarily in student dormitories or temporary housing are sampled within the households that they reside in permanently. Persons excluded from the universe are those with no fixed household address (e.g., homeless and/or transient persons not residing in shelters), active duty military personnel and civilians living on military bases, persons in long-term care institutions (e.g., nursing homes for the elderly, hospitals for the chronically ill or physically or intellectually disabled, and wards for abused or neglected children), persons in correctional facilities (e.g., prisons or jails, juvenile detention centers, and halfway houses), and U.S. nationals living in foreign countries. While active-duty Armed Forces personnel cannot be sampled for inclusion in the survey, any civilians residing with Armed Forces personnel in non-military housing are eligible to be sampled.
Because the NHIS is conducted in a face-to-face interview format, the costs of interviewing a large simple random sample of households and noninstitutional group quarters would be prohibitive; randomly sampled dwelling units would be too dispersed throughout the nation for cost-effective interviewing. To keep survey operations manageable, cost-effective, and timely, the NHIS uses geographically clustered sampling techniques to select the sample of dwelling units for the NHIS. The sample is designed in such a way that each month’s sample is nationally representative. Data collection on the NHIS is continuous, i.e., from January to December each year.
The sampling plan is redesigned after every decennial census. A new sampling plan for the 2016–2025 NHIS was designed with results of the 2010 decennial census. Commercial address lists are used as the main source of addresses, supplemented by field listing. The annual sample size can be reduced or increased as needed.
The content and structure of the NHIS were updated in 2019 to better meet the needs of data users. Aims of the questionnaire redesign were to improve the measurement of covered health topics, reduce respondent burden by shortening the length of the questionnaire, harmonize overlapping content with other federal health surveys, establish a long-term structure of ongoing and periodic topics, and incorporate advances in survey methodology and measurement.
One “sample adult” aged 18 years or older and one “sample child” aged 17 years or younger (if any children live in the household) are randomly selected from each household following a brief initial interview that identifies everyone who usually lives or stays in the household. Information about the sample adult is collected from the sample adult herself or himself unless she or he is physically or mentally unable to do so, in which case a knowledgeable proxy can answer for the sample adult. Information about the sample child is collected from a parent or adult who is knowledgeable about and responsible for the health care of the sample child. This respondent may or may not also be the sample adult.
From 1997-2018, the NHIS also included a family questionnaire. Questions from the family questionnaire, including questions on health insurance and unmet needs for medical care, were answered by a member of the family on behalf of all members of the family. In the redesigned survey, much of the content that was collected about the sample adult and sample child in the family section is now collected within the sample adult and sample child questionnaires, from the sample adult or sample child’s respondent rather than another family member. Sample adults may give different answers about themselves than would a family member responding for them, and this could impact survey estimates.
The elimination of the family questionnaire in 2019 was one part of an effort to shorten the length of the questionnaire. In addition, questions on rare conditions or service utilization (those with less than a 2% prevalence), questions on topics that were no longer priorities, and questions that were rarely used in analysis were dropped. A structure of annual and rotating content was also implemented in 2019. The annual core contains the same questions from year to year, and these questions focus on demographic characteristics, health insurance, chronic conditions, health care access and use, health-related behaviors, and functioning and disability. The rotating core consists of questions that will be included in the interview periodically and include expanded content on mental health, service utilization, preventive services, health-related behaviors, injuries, and chronic pain. The periodicity of questions in the rotating core varies by question and may be every-other year, once-every-three years, or two-out-of-three years.
As a result of dropping questions and putting others on a rotating schedule, along with the addition of new questions reflecting new priorities, the question order and the context of most questions (that is, the questions that come immediately before) changed with the questionnaire redesign. These changes can affect how subsequent questions are interpreted and responded to, and these effects could impact survey estimates. Data users looking at trends before and after the questionnaire redesign should carefully consider the impact of these changes.
The U.S. Census Bureau, under a contractual agreement, is the data collection agent for the National Health Interview Survey. NHIS data are collected continuously throughout the year by Census interviewers. Nationally, about 750 interviewers (also called “Field Representatives” or “FRs”) are trained and directed by health survey supervisors in the U.S. Census Bureau Regional Offices to conduct interviews for NHIS.
The NHIS is conducted using computer-assisted personal interviewing. Face-to-face interviews are conducted in respondents’ homes, but follow-ups to complete interviews may be conducted over the telephone. A telephone interview may also be conducted when the respondent requests a telephone interview or when road conditions or travel distances would make it difficult to schedule a personal visit before the required completion date. In 2019, 34.3% of the Sample Adult interviews and 31.7% of the Sample Child interviews were conducted at least partially by telephone.
Information from NHIS is made available through an extensive series of NCHS Data Briefs, National Health Statistics Reports, MMWR Quickstats, and publications and articles in scientific and technical journals. Selected estimates are also available as part of an interactive data query system that provides tables and charts. These estimates are available for the nation as a whole and for selected subgroups defined by characteristics such as sex, age, race, ethnicity, family income, and region of the United States.
For data users and researchers throughout the world, survey data files are available on the internet. Analysts are reminded that NHIS is a sample survey. That is, only a sample (subset) of the civilian noninstitutionalized population is selected to participate in the survey. Sampling weights must be used to produce representative national estimates. More information for analysts about the proper use of the survey data files is available in the annual Survey Description documents by data year.