OCC records the person's primary occupation, classified according to the system used by the respective national census office at the time. For someone with more than one job, the primary occupation is usually the one in which the person spent the most time or earned the most money, although this may not have been explicit in the instructions for a specific census.
To ensure confidentiality, very small occupations are recoded to a residual category indicating the persons had an occupation, but the job title is not identified. The number of cases recoded should be too small to affect analyses.
Work Variables -- PERSON
Imputation and derivation
OCC is a 4-digit numeric variable.
Some samples use fewer than 4 digits. In those cases, the data are right-justified, and the extra leading digits are padded with zeroes.