The National Health Interview Survey (NHIS) is an annual, cross sectional household interview survey of the civilian non institutionalized U.S. population conducted by the National Center for Health Statistics (NCHS) within the Centers for Disease Control and Prevention (CDC). What it contains: - Individual level data on a wide range of health topics including chronic conditions, health behaviors, access to care, insurance status, disability, and demographic variables. - Specialized modules (e.g., asthma, tobacco use, mental health) that rotate or appear as sponsored content each year. - Sample adult and child interviews with detailed questionnaire responses, sample weights for population level estimates, and ancillary files (imputed income, paradata). Purpose & use cases: - To monitor national trends in health status, disease prevalence, and health care utilization. - Provides a foundation for public health surveillance, policy evaluation, epidemiologic research, and the development of health indicators (e.g., Healthy People objectives). - Frequently used by researchers, government agencies, and NGOs to assess disparities across age, race/ethnicity, socioeconomic groups, and geographic regions. Key features / unique aspects: - A probability based, geographically clustered sampling design that yields a nationally representative sample each year. - Continuous data collection (January-December) with yearly updates, allowing timely trend analysis. - Extensive documentation (questionnaires, SAS/SPSS/Stata input files, weight variables) and publicly available datasets for free download. - The survey's rotating core content and sponsor driven modules make it adaptable to emerging health issues while maintaining a consistent longitudinal backbone.