I would like to estimate country differences in earning for university graduates. I know I could use the real PPP GDP for that, but I would specifically like the average wage per country for someone who has a tertiary degree. I have found the earnings data from the ILO, which is sorted into the ISIC classifications by occupation. However, I have no clue how to figure out who should have a tertiary degree with these classifications. Their documentation is not helpful at all. Does anyone have a dataset or an idea how to convert ISIC Rev. 4 (or older) classifications to ISCED classifications? Roughly is enough.