How do IHIS files differ from the NHIS public use files already in distribution?
Public use files for the core survey and supplements of the NHIS are the basis for IHIS data. These original public use files also include supplements and variables not included in the current IHIS data release. Researchers can access the original files here. Directions on how to link variables from these original NHIS public use files to IHIS data extracts can be found in the user note on linking. The IHIS Project recodes the original public use data to increase consistency over time. IHIS also provides on-line documentation that describes variable meaning, question wording, and comparability issues, along with information about years available and codes and frequencies for each included variable. By using the IHIS data extraction system, analysts can select the years and variables they are interested in and work with a single dataset, without having to link or combine multiple files. For the most part, IHIS does not use the same variable names included in the original public use data
