Integrated Health Interview Series (IHIS): Providing free, integrated NHIS data over the Internet

The National Health Interview Survey (NHIS) has been fielded annually since 1957 and is the leading nationally-representative source of information on the health of the U.S. population. Beginning in the 1970s, the National Center for Health Statistics (NCHS) released public use NHIS data files on tape; beginning in 2001, NCHS provided downloadable data and documentation files over the Internet. Because of difficulty associated with manipulating multiple files, integrating inconsistently named and coded variables, and navigating thousands of pages of annual documentation, most research and publications use NHIS from a single year. With NIH funding, researchers at University of Minnesota created the Integrated Health Interview Series (IHIS), a consistently-coded, fully-documented version of NHIS data accessible for free over the Internet. Using cutting-edge information technology, integrated metadata, and customized programming, we created a system in which researchers can: 1) evaluate and search the full range of variables and topics across time; 2) view variable-specific codes and frequencies, question wording, universes, appropriate weights, and discussions of meaning and comparability issues; 3) learn NHIS variable names and source files for IHIS variables; 4) create a tailor-made extract containing the years and variables relevant to their research. By the end of 2010, IHIS will provide access to over 10,000 harmonized variables and vastly simplify analysis of the full topical and temporal richness of NHIS data.