I have a big dataset, with variables at the industry level. This dataset is presently at either the NAICS 1997 classification, or the SIC 1987 classification. I want to merge this dataset with an existing dataset which contains industry level data at the 3 digit ISIC Rev 2 level. The former (either NAICS or SIC) contain 400+ distinct sectors, whereas the ISIC contains only 28. As such, there should be a many to one mapping from either of the former to the ISIC Rev 2. I am unable to find concordance tables between either the NAICS or SIC to the ISIC Rev 2 (specifically 3 digit) classification.
Any help is much appreciated.