NHISHID is a 14-character string variable.
NHISHID is an IPUMS NHIS-constructed value that is an identifying number unique to each household in a given survey year. Using NHISHID, analysts can link IPUMS NHIS data with additional household-level data elements, from the NHIS source public use data files, that are not currently available in IPUMS. NHISHID is a single variable constructed by concatenating multiple data elements from the NHIS source data files. Analysts wishing to link person-level NHIS data should use the person-level linking key NHISPID.
See the user note on LINKING for instructions on how to create links between IPUMS NHIS and NHIS source data.
After the 2019 redesign, there is no longer a sampling weight to produce household population estimates. See the user note on the calculation and use of sampling weights for additional information.
The variables concatenated to construct NHISHID differ by periods. There are four discrete periods, namely: 1) 1968-1991 and 1993-1994; 2) 1992; 3) 1995-1996; and 4) 1997-forward. While the particular combination of variables used to construct NHISHID differs between these periods, the substantive meaning of the variable is consistent across years. In the discussion that follows, the elements of NHISHID are identified via the variable names used in the original NHIS public use data source files.
The sequential elements in NHISHID before 1994 (except for 1992) are processing quarter (QUARTER), PSU number (PSUNUMR), census week (WEEKCEN), segment number (SEGNUM), and household number (HHNUM).
The sequential elements of NHISHID for 1992 are processing year (YEAR), processing quarter (QUARTER), PSU number (PSUNUMR), census week (WEEKCEN), segment number (SEGNUM), and household number (HHNUM).
The only element of NHISHID for 1995 and 1996 is household ID (HHID).
For 1997 forward, the sequential elements of NHISHID are processing year (YEAR) and household serial number (HHX).
The NHIS questionnaire was substantially redesigned in 2019 to introduce a different data collection structure and new content. Beginning in 2019, HHX, a component of NHSIHID, leads with the character "H" followed by six numeric digits. Prior to 2019, HHX consisted only of six numeric digits. This does not change the fact that NHISHID is unique within a sample. For more information on changes in terminology, universes, and data collection methods beginning in 2019, please see the user note. One of the most notable changes introduced in 2019 is that a maximum of one adult and one child are sampled per household, so that there are only up to two persons affiliated with any given household.
- 1963-2018: All households (NHIS samples).
- 2019: Sample adults age 18+ and sample children age 0-17.
- 1963, 1966-1967, 1969-2018 : HHWEIGHT