Using CPS 1962-69, why is occ1990 missing except for 1968 ad 1969?

#1

Using CPS 1962-69, why is occ1990 missing except for 1968 ad 1969?

#2

The OCC1990 variable is only available beginning with the 1968 ASEC sample. The occupational codes used in the CPS prior to 1968 were substantially different than in later years. Specifically, they were only two digits and there were fewer than 40 categories. After 1968, occupational codes were expanded to three digits and well over 200 categories. Due to the lack of detail in the pre-1968 occupational codes, expanding OCC1990 to these samples would be problematic.

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