Hi Colin,
JBISCO88 is coded from JBSOC00, JBSEMP, JBSIZE and JSSIZE using rigid look-up files, see e.g. https://www.understandingsociety.ac.uk/documentation/mainstage/dataset-documentation/variable/jbisco88. I am not exactly sure what you mean by bias? Do you mean a coding error?
I can confirm that JBISCO88_CC 122 and 123 codes are the most frequent codes (in W1 and W9). Cases with JBISCO88_CC 122 or 123 should have JBSOC00_CC codes that indicate managerial positions and this is what I find in the data, too: The current job SOC 2000 codes have the expected JBSOC00_CC codes (112-118, 121-123). The most prevalent JBSOC00_CC code (in W1 and W9) appears to be 113 "Functional managers'. The ONS's SOC 2000 guide shows this covers managers in sales, marketing, finance and IT.
Generally, it does not strike me as odd that these occupations are frequent as these are big industries/occupations in Britain and the number of people who describe their jobs as involving some sort of 'managment' (e.g., of projects, however, small they may be; or of people, however few they may be) these days is likely high. Are the population estimates you get for SOC 2000 from Understanding Society not comparable with other official statistics?
Thanks,
Gundi
On behalf of Understanding Society User Support