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Simple industry classification (2004 forward, NAICS)

Codes and Frequencies

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For sample adults aged 18 and older who were working at a paying or non-paying job last week, who were with a job or business but not at work, who were working but not for pay at a family-owned job or business, or who have ever worked, INDSTRN204 reports the person's industry, grouped into 21 major industry groups. Please refer to the code tab for more information on different industrial categories.

INDSTRN204 provides a simple list of 21 major industry groups while INDSTRN104 provides a detailed list of 79 industry subgroups. INDSTRN204 and INDSTRN104 correspond to the 2000 Standard Industry Classification (2000 SIC) major groups and subgroups, respectively, as determined by the U.S. Census Bureau and the Bureau of Labor Statistics.


This variable was introduced in 2004 as part of the Adult Socio-Demographics (ADS) section, which provides information on occupation, industry, workplace, and employment conditions of currently employed sample adults as well as those who have ever worked.

The ASD section underwent major recoding issues due to changes in the U.S. economy, which led to changes in industry classifications. Prior to 2004, industry classification in the NHIS data was based on 3-digit codes assigned by the U.S. Census Bureau. These codes are consistent with the structures of the 1987 Standard Industrial Classification (SIC), but not actually SIC codes. NHIS used to include these 3-digit codes in the public use data files prior to 1997. However, due to concerns about confidentiality, NHIS started to store these 3-digit codes in their in-house files and assigned 2-digit recodes to the industry classification in the public use files.

Due to changes in the U.S. economy, the 1987 SIC were replaced by the North American Industrial Classification System (NAICS) and a revamped SOC. As a result, the U.S Census Bureau developed a new set of 4-digits codes that are consistent with the 2000 SIC. To ensure comparability, the NHIS in-house files contain both 3-digit and 4-digit codes for industry classification. The 3-digit codes are consistent with the structures of the 1987 SIC, while the 4-digits codes are comparable to the 1997 NAICS and 2000 SOC. For confidentiality reasons, public use files also contain two sets of 2-digit codes for industry classifications, one set is based on the new 4-digit Census codes and the other is based on the 3-digit Census codes.

For more information about the ASD section and other related variables, please use the IPUMS NHIS search function and drop-down menus.


There are no comparability issues with INDSTRN204 because the universe and response categories for this variable are consistent from 2004 and forward. However, researchers are strongly discouraged to compare simple industry recodes based on the 2000 SIC to simple industry recodes based on the 1987 SIC because they are entirely different classification systems; therefore, the recodes are not comparable. Researchers are advised to only compare simple industry codes that use the same classification system. The 1987 SIC/SOC recodes were discontinued in 2005 and were replaced completely by the 1997 NAICS/2000 SOC.


  • 2004-2018: Sample adults are 18+ who were working at a paying or non-paying job last week, who had a job or business but were not at work last week, or who had ever worked.


  • 2004-2018