The National Health Interview Survey (NHIS) is an annual, cross-sectional survey intended to provide nationally-representative estimates on a wide range of health status and utilization measures among the nonmilitary, noninstitutionalized population of the United States. Each annual data set can be used to examine the disease burden and access to care that individuals and families are currently experiencing in the United States.
NHIS is designed by the CDC's National Center for Health Statistics (NCHS) – the government agency tasked to monitor the population's health status and behavior – and administered by the U.S. Census Bureau.[1] NHIS has been administered since 1957, although the core content and questionnaires undergo major revisions every 10–15 years.[2] NHIS allows both governmental and outside researchers to obtain estimates on a variety of health-related topics among either the entire nation or specific demographic groups of the population. Also, since the survey design is cross-sectional rather than longitudinal, health information can be trended for demographic groups and the country as a whole, but not for individuals or families.
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Authorized by the National Health Survey Act of 1956[3], the U.S. Public Health Service was tasked with implementing an annual survey to collect information on morbidities – physical or mental conditions related to any illness or injury – and medical service and medical facility utilization. The most recent re-design of the survey questionnaire was implemented in 1997.
NHIS data contain information on health, influences on health, and health outcomes, as well as common demographic indicators to give users the ability to examine health status, behavior, and risk factors within and across subsets of the population (such as racial and ethnic health disparities).
The major health topics covered in the Core questionnaires include health status, insurance coverage, complementary and alternative medicine, use of health services, immunizations, health behaviors, injuries, occupational health, cancer screening, ability to perform daily activities, and conditions such as asthma, diabetes, mental health.[4] NCHS continually produces chart books, statistical briefs, and fact sheets using NHIS data which shed light on these various facets of morbidities and how the American populace behaves in response.
Periodically, the NHIS includes supplemental questionnaires regarding a focused topic that might be of particular current interest. For example, a cancer supplement was fielded in 1987, 1992, 2000, 2003, 2005, 2008, and 2010, and sponsored by the National Cancer Institute and the National Center for Chronic Disease Prevention. This supplement included questions about cancer screenings, diet, exercise, smoking, sun exposure, and family history.[1] A full list of supplements can be found on the NHIS website.
The National Health Interview Survey is commonly the subject of analysis in articles on health status and health behaviors in research journals such as Obesity, Journal of the American Dietetic Association, Health Services Research, and the American Journal of Public Health.[5]
A number of CDC reports, including Healthy People, rely on NHIS to monitor health estimates.
The Department of Health and Human Services (HHS), Office of the Assistant Secretary for Planning and Evaluation (ASPE) tracks health insurance coverage in the United States using the NHIS.[6]
The National Center for Health Statistics publishes periodical statistical summaries,[7] compiling the results of the most recent NHIS and trending those statistics over time for certain groups.
NCHS/CDC also publish statistical reports on current topics of interest,[8] and shorter data briefs.[9]
Noninstitutional civilian Americans (both citizens and non-citizens) are sampled by household, allowing for analysis of medical behavior at the family-level. After a household has been sampled, one adult and one child (if any are present) is selected to complete the Sample Adult and Sample Child components of the survey. In years without budget cuts, approximately 35,000 households containing 87,500 individuals are included.[2]
NHIS follows a multi-stage area probability design, meaning that geographic areas – rather than unique households – are sampled first, and then within those selected areas, residences are sampled. Unlike surveys with a panel or longitudinal design, the entirety of data collected from each household occurs from a single interview lasting about an hour.[2]
The complex survey design must be analyzed with software capable of handling survey data that was not obtained from a simple random sample, such as R, SUDAAN, SAS, Stata, SPSS, and VPLX. In addition to appropriately weighting households that might have been over-represented in the raw data (due to oversampling of populations of interest), survey analysis packages are needed to employ the Taylor-series linearization technique to correctly calculate the standard errors and confidence intervals.[10]
The Medical Expenditure Panel Survey currently uses the NHIS sampled population to form its own sampling frame (ultimately sampling one-half of NHIS respondent households for its own publicly-available complete survey).[2] After filling out a confidentiality agreement, AHRQ provides a crosswalk to merge these data together.[11]
NHIS data can also be linked to death certificates in the National Death Index (NDI).