I am interested in exploring the percentage of workers who are in unions in Chicago since 1990, and potentially breaking it down further by occupation. I am using annual ASEC samples from IPUMS CPS for the years 1990, 2000, 2010, 2020 and 2025. I also am applying the EARNWT weight for the UNION variable. What is strange is that the percentage of union members I am getting is much lower than published BLS statistics on this (which are taken from CPS data). For instance, according to BLS data, 16% of US workers were unionized in 1990, but when I tabulate this using my annual samples for the whole US, I get 8.78% union members and 1.27% covered by a union contract, which added together is still far less than 16%. I should add that I am excluding self-employed and unemployed workers, so only current wage or salary workers should be in this total. Any ideas what could be going wrong here? Thanks!
I suspect that the source of your discrepancy is in the inclusion of persons who are not in the universe for UNION.
The variable UNION assigns all persons in the data to one of four codes:
- 0: “NIU” (Not in Universe)
- 1: “No union coverage”
- 2: “Member of labor union”
- 3: Covered by union but not a member"
The Universe tab for UNION states that the universe for UNION is:
Civilians 15+ currently employed as wage/salary workers and in 2 (out of 8) rotation groups. Excludes self-employed persons.
All persons who do not fit into this universe definition are assigned UNION = 0. When including all four of these codes, I am able to replicate your 8.7% union coverage estimate. However, since all four codes are included, this estimate reports the percentage of all persons who are a member of a union rather than the percentage of all workers. You note that you exclude self-employed and unemployed workers, but your estimate appears to still include many not in universe cases. An easier option is to exclude all cases of UNION = 0 from your analysis. When I do this using the IPUMS CPS Online Analysis Tool, the estimate that I get is that 15.9% of all persons in the universe for UNION are members of a labor union. In the screenshot of the online tool below, I selected to analyze all CPS BMS samples. I then included the filters “year(1990)” and UNION"(1-3)".
While some people who do not fit the universe (such as self-employed persons) might be members of a labor union, no data on these people’s union membership was collected. Note also that excluding everyone with UNION=0 is different from excluding self-employed and unemployed people because the universe of UNION is more restrictive than that since it also excludes non-civilians and those who do not work for a wage or salary.
Thank you so much! That makes perfect sense. I am able to get more accurate percentages now.