The National Health Interview Survey (NHIS), conducted by the National Center for Health Statistics (NCHS), is a multipurpose health survey and the principal source of basic information on the health of the civilian noninstitutionalized household population of the United States. It is a cross-sectional, nationally representative sample with reliable estimates for the four defined geographic regions of the United States.
The NHIS consists of a core or basic module as well as variable supplements. The basic module consists of three components: the family core, the sample adult core, and the sample child core. The family core component collects information on everyone in the family, including household composition and sociodemographic characteristics; tracking information; information that matches administrative databases and basic indicators of health status; activity limitations, injuries, health insurance coverage, and access to, and use of, health care services. For each family in the NHIS, one sample adult and one sample child (if any children under age 18 are present) are randomly selected and information is collected on their health status, health care services, and behavior with the specific core questionnaires.
For the family core questionnaire of the basic module, all members of the household age 18 and over who are at home at the time of the interview are invited to participate and to respond for themselves. For children and adults not at home during the interview, information is provided by a knowledgeable adult residing in the household. For the sample adult questionnaire, one adult per family is randomly selected; this individual responds for himself or herself, unless physically or mentally unable to do so. Information for the sample child questionnaire is obtained from a knowledgeable adult residing in the household. Topical modules are fielded less frequently.
About 40,000 households are interviewed annually, including approximately 112,000 people of whom 29,000 are under age 18. The interviewed sample for 2004 consisted of 36,579 households, which yielded 94,000 persons in 37,466 families. The interviewed sample for the sample child component, by proxy response from a knowledgeable adult in the family, was 12,424 children under age 18. Interviewing is conducted continually, so that seasonality can be studied from any systematic month-to-month variation over the year and the effects of seasonality can be averaged out.
NHIS is not currently designed to provide state-level estimates. However, black and Hispanic populations are oversampled now to allow more precise estimation of health in these growing minority populations.
A possible problem is that the NHIS is faced with periodic budgetary shortfalls, as occurred in 2002, 2003, and 2004. As a result, NCHS reduced the size of the NHIS sample in these years. Since grouping the sample cuts