intervals. Linkage to other health surveys 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). After filling out a confidentiality agreement, AHRQ provides a crosswalk to merge these data. NHIS data can also be linked to death certificates in the National Death Index (NDI). Data Available NHIS data are freely downloadable by the public, and generally become available in June or July for the preceding year's data set. Certain variables that might make survey respondents easily identifiable (such as geographic locations, exact dates of events and procedures) are not available from the publicly available data, but can be accessed and analyzed by applying for access to the NCHS Research Data Center. The current publicly available annual National Health Interview Survey data release consists of four files which describe the demographics and health-related characteristics of the survey population at the household, family, and person-level, as well as two files designed to capture information on any injuries experienced during the year. Core Household File With one record per household in the sample, this file mainly contains descriptors necessary to determine the number of individuals and families within each sampled household, and allows researchers to link families or other unrelated individuals captured in any of the other Core files based on household of residence (using the HHX variable). This file also contains basic information on non-response and a household-level final weight. Family File This file contains one record per family in the sample, with general information on identifiers (such as family member age, race, family structure, family income), health status and limitations, injuries and poisonings, access to care and utilization, and health insurance. The family file can be linked to other files containing information on adults and children within each family (using the HHX and FMX variables). Person File This file contains information on every individual within every family within every household selected for participation in the NHIS. Survey data about individuals who were either not available at the time of the interview or under 18 were provided by an available adult in the household. This person-level file contains information on health status and limitation of activity, health care access and utilization, health insurance, socio-demographics, and income and assets. Examining this file using the final weight variable (WTFA) generalizes to the