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Stratum for variance estimation


STRATA is a 5-digit numeric variable.

000: Not in Universe


STRATA is an IPUMS NHIS-constructed variable based on the NHIS sample design variables in the public use files concatenated with a sample design period indicator. STRATA represents the impact of the sample design stratification on the estimates of variance and standard errors. It is constant within a sample design period and changes between sample design periods. For analysis, researchers need to use STRATA in conjunction with PSU to account for stratification and clustering when computing variance estimates with IPUMS NHIS data.

See the User Notes on variance estimation for additional information.

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.


This variable is generally comparable for 1985 forward but may be affected by changes in the 2019 redesign.

For 1969-1984, the variance estimates will not take into account the efficiencies that were likely gained from stratification in these years. Consequently, analyses done as the data are currently structured will have standard errors that are slightly biased upward for this time period (i.e., too large). We are currently working to incorporate recently released strata information for the early years, so that analysts using IPUMS NHIS data can more appropriately compute standard errors for all years of data.

The NHIS questionnaire was substantially redesigned in 2019 to introduce a different data collection structure and new content. For more information on changes in terminology, universes, and data collection methods beginning in 2019, please see the user note.


  • 1963-2018: All households.
  • 2019-2022: Sample adults age 18+ and sample children age 0-17.


  • 1963-2022