How do IHIS files differ from the NHIS public use files already in distribution?
Public use files for the NHIS are the basis for IHIS data. These original public use files also include variables not yet included in the IHIS public database. Researchers can access the original files through the IHIS website. 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. For the most part, IHIS does not use the same variable names included in the original public use data; variables have been renamed to increase consistency over time and within subject categories. Detail from the original public use variables is preserved in IHIS integrated variables, but codes and value labels are often different in the IHIS version of a variable. For a crosswalk between the original NHIS public use variable names and the IHIS variable names, use the IHIS-NHIS variable concordance (as a search tool or downloaded into an Excel file).