I’m trying to use OCC1990 to serve as consistent measure of employment numbers across differen occupations from 1950 to 2022. However, I’m noticing that in a lot of occupations, there will be some codes that appear in some years but some that don’t. So essentially, there are some jobs that are just not matched across time and “disappear”. I thought the point of OCC1990 was to resolve that? Is there any way to figure out what “happened” to the jobs that disappear?
The purpose of OCC1990 is to assign occupations throughout the IPUMS samples to a single occupation classification system to help researchers analyze occupation over time. This assignment process is complicated because occupation groups from a classification system in one year will not perfectly match into groups in the system for a different year. For example, math instructors (OCC1990 = 128) are identified in the 1990 Census with OCC = 128. However, in the 2000 Census, math instructors are not independently identified. Instead, the 1990-2000 Census Occupation Crosswalk notes that math instructors in this year are included in OCC = 220 (“postsecondary teachers”). Since particular subjects of instruction are not identified, there cannot be any respondents with OCC1990 = 128 in the 2000 sample.
IPUMS provides an in-depth discussion of the process used to create harmonized occupation and industry codes. Users should be aware that in producing these harmonized codes, IPUMS traced the proportion of each occupation as it broke out into more specific occupations or as it was combined with others into a more general occupation. A modal assignment rule was used where occupations were assigned into the code that a plurality of its members would have been coded into.
To take one example from the technical paper produced after the 1970 census: of persons coded as “Archivists and curators” in 1970, the Census Bureau determined that 60% would have been coded as “Miscellaneous social scientists” in 1960, while 40% would have been coded as “Professional, technical, and kindred workers, not elsewhere classified.” The crosswalk from 1950-1960 then shows that the plurality of persons – those coded as “Miscellaneous social scientists” in 1960 – would have been coded as “Miscellaneous social scientists” in 1950. Thus, OCC1950 codes all “Archivists and curators” in the original 1970 occupational classification to "Miscellaneous social scientists.
Researchers have the option to use other covariates (e.g. sex or education) to create their own occupation crosswalk to assign harmonized occupation codes instead of only using the total conversion rate.