Are there aspects of IHIS data about which to be particularly careful?
IHIS is an integrated dataset based on the NHIS public use files. However, IHIS coding schemes follow different conventions than NHIS in many instances. For example, NHIS uses the convention of 1 = Yes and 2 = No, while IHIS uses the convention 1 = No and 2 = Yes. To pick another example, blanks in the original NHIS public use data files are converted to numeric values (usually beginning with a 0 or a 9, to indicate “not in universe” cases) in IHIS. Moreover, to achieve comparably coded variables over time, IHIS has recoded most variables from the original NHIS coding schemes. Users are strongly urged to review the IHIS documentation carefully and to not assume that variable values will be coded the same in IHIS as they were in the NHIS files. The NHIS uses a complex sampling scheme, so all IHIS samples are weighted. Put another way, individuals in the data do not all represent an identical number of persons in the population in a given year. It is therefore necessary to use the approp
