Codes and Frequencies
IND1995 is a modified version of the 1995 revised Standard Industrial Classification-based codes (SIC), offering researchers a consistent long-term classification of industries from 1969 to present. All original industry codes are available in IND. For more information on all of the industrial schemes that were used in previous NHIS surveys, please refer to the "User Note on Occupation and Industry Variables". Please see the "Universe" tab for more detailed information on changes in the universe across survey samples.
Industry coding in NHIS surveys underwent its two biggest changes in 1983 when the NHIS switched from using the 1967 SIC to the 1972 SIC, and in 2004 after the 2002 North American Industry Classification System (NAICS) was released. The introduction of the 1972 SIC and the 2002 NAICS contributed to significant discontinuities in industry coding in the NHIS history. The IPUMS NHIS staff chose the 1995 revised SIC as the standard because it falls in-between the years when the 1972 SIC and the 2002 NAICS were implemented in the NHIS.
The construction of IND1995 is based on the work done by the IPUMS-USA project, which harmonized Census Bureau industry classifications from 1950 to present, using the 1990 Census Bureau industry classification scheme as a standard. Based on a series of technical papers and crosswalks that provide detailed analyses on how the industry coding scheme for each census year differed from the scheme used in the previous census year, the IPUMS staff traced the proportion of each industry as it broke down into more specific industries or as it was combined with others into a more aggregated industry.
The IHIS followed procedures established by IPUMS-USA staff to create a version of the industry codes that is comparable, to the extent possible, to the 1995 revised SIC that was used in NHIS surveys from 1995 to 2003. However, IHIS staff were not able to follow the exact procedures employed by IPUMS-USA staff because the NHIS released far less detail on industry codes on the public use files than the Census or American Community Survey. For example, in the 2010 sample, the NHIS industry code "71" (amusement, gambling, and recreation industries) combined multiple industries that were distinct in the Census, including code "8580" (bowling centers) and code "8590" (other amusement, gambling, and recreation centers).
Changes in the universe across years limit the comparability of this variable.
From 1969 to 1996, the universe included sample persons aged 17 and older (1969-1981 samples) and sample persons aged 18 and older (1982-1996 samples) who were in the labor force in the past 2 weeks. According to the Interviewer's Manual, being in the labor force means that the person is currently working, is temporarily absent from a job, or is looking for work. From 1997 to 2003, the question was asked of sample persons aged 18 and older who were working at a paying job last week, were with a job/business but not at work, or were working at a non-paying job last week. The universe from 2004 forward is similar to that of the 1997-2003 samples, except that people who have ever worked are now also included in the universe. Users wishing to increase the comparability of IND1995 should use WORKEV to exclude persons who have ever worked and are not currently employed.
- 1969-1981: Persons age 17+ who were in the labor force (working, temporarily absent from a job, or looking for work) during the past 2 weeks.
- 1982-1996: Persons age 18+ who were in the labor force (working, temporarily absent from a job, or looking for work) during the past 2 weeks.
- 1997-2003: Sample adults aged 18 and older who were working at a paying job last week, with a job or business but not at work, working at a non-paying job last week.
- 2001-2017: Sample adults aged 18 and older who were working at a paying job last week, with a job or business but not at work, working at a non-paying job last week, or who had ever worked.