I have a question about the variable educ in IPUMS-CPS. When I plot the percentage of individuals having a high school degree (educ=73) over time I see a big increase in 1992. I see a similar pattern for college or more (educ>110) as well as a reverse pattern for strictly less than high school education (educ<73) and some college (80<=educ<=110). If I plot the percentage of individuals with high school or less (educ<=73) or individuals with more than high school (educ>73) over time, I don’t see big jumps and the time series are smooth. I think it has to do with the change in 1992 from highest grade attained to completed degree. So, I just wanted to make sure that my thinking is correct, and that the only educational categories that can be used consistently over time are high school or less (educ<=73) and individuals with more than high school (educ>73).
Your thinking is correct about this, although there are more comparable categories available beyond “HS or less” and “more than HS.” The comparability page for EDUC notes:
To maximize comparability across time, users should use only the first two digits of EDUC. In all years, these two digits will indicate the highest grade or year of schooling completed through the end of high school.
Prior to 1992, while it is known how many years of higher education was completed, there is no way to know definitively whether completing these years resulted in a degree.