User Note - Occupation and Industry Variables
Occupation and industry are collected as part of the core person questionnaires prior to 1997 and as part of the Adult Socio-Demographic (ASD) section from 1997 forward. Verbatim responses with detailed information on specific functions of the person's job and the person's employer were recorded by NHIS interviewers. These verbatim responses were later reviewed by U.S. Census Bureau coding specialists, who assign appropriate 3-digit (prior to 2004) or 4-digit (2004-onward) occupation and industry codes. These codes are informed by the Standard Occupation Classification (SOC) or the Standard Industry Classification (SIC)/North American Industry Classification System (NAICS), but are not the actual SOC codes or SIC/NAICS codes. In order to protect the confidentiality of respondents, NHIS staff removed the detailed 3-digit and 4-digit codes from the public use NHIS files and replaced them with 2-digit recodes for both occupation and industry classifications.
In 2000, the Census moved to the North American Industry Classification System (NAICS), which was developed to allow for a high level of comparability in business statistics across North American countries. For consistency with the new NAICS, the Census revised the SOC, producing the 2000 revised SOC (or the New SOC). These new NAICS and SOC codes were 6-8 digits in length. Based on the detailed NAICS and SOC codes, the Census developed new coding systems for non-economic federal surveys such as the NHIS that contain no more than 4 digits. Beginning in 2004, the NHIS began using these 4-digit codes for occupation and industry classifications in their in-house files and publishing the recoded 2-digit codes in the public use NHIS files. As mentioned in the NHIS survey description in 2004, the new NAICS/2000 revised SOC are not directly comparable to previous SIC/SOC systems because they use different classification schemes. The introduction of the NAICS and the 2000 revised SOC in 2004 constituted the biggest discontinuity in industrial and occupational coding in the entire NHIS history. In addition, the Census Bureau has modified its classification systems each decade, which affects the comparability of occupation and industry variables over time in the NHIS. Therefore, long-term studies of occupations and industries typically require extensive reconciliation of codes.
Reconciled and Original Occupation and Industry Codes in IPUMS NHIS
Although a complete reconciliation of these coding schemes is impossible, we provide variables that maximize the potential for consistent comparisons of occupational status and industry. Using procedures developed by IPUMS-USA staff, based on guidance from technical reports and crosswalks produced by staff at the Census and the Bureau of Labor Statistics, IPUMS staff reconciled NHIS occupation and industry codes over time. The result of these efforts is the variables OCC1995 and IND1995. OCC1995 codes occupations from 1969 and onward into the 1995 revised SOC-based codes. OCC1995 allows researchers to use a consistent classification scheme to locate persons in the occupational/social structure. IND1995 accomplishes the same for industrial classifications.
For more detailed information on how OCC1995 and IND1995 were created, please refer to the variable descriptions for these two variables on our website. IPUMS NHIS also retains all original occupation and industry information in the OCC and IND variables.
Changes in the NHIS Occupation and Industry Coding Schemes over Time
There are seven major occupational coding schemes in the original NHIS files. NHIS occupation input codes were informed by the 1960 Classified Index of Occupation from 1969 to 1970, the 1970 Classified Index of Occupation from 1971 to 1982, the 1977 SOC from 1983 to 1991, the 1992 revised SOC from 1992 to 1994, the 1995 revised SOC from 1995 to 2003, the new SOC (or the 2000 SOC) from 2004 to 2009, and the 2010 SOC from 2010 forward. Because the SOC system came out in 1977, all occupation codes in the NHIS prior to 1983 were informed by the Classified Index of Occupation, which was developed by the Census. Please refer to the Occupation Coding Guidelines for more information on the Classified Index of Occupation.
Similarly, there are also seven industrial coding schemes in the NHIS files. NHIS industry input codes were informed by the 1957 SIC from 1969 to 1970, the 1967 SIC from 1971 to 1982, the 1972 SIC from 1983 to 1991, the 1992 revised SIC from 1992 to 1994, the 1995 revised SIC from 1995 to 2003, the 2002 NAICS from 2004 to 2007, the NAICS 2007 from 2008-2013, and the NAICS 2012 from 2014 to the present. The meaning of occupational and industrial classifications changed across these major schemes, which limits the comparability of occupations or industries across NHIS surveys.