Also, secretary was a category that covered job descriptions ranging from phone operator to business analyst. Factory worker probably covers as much variation

Also, secretary was a category that covered job descriptions ranging from phone operator to business analyst. Factory worker probably covers as much variation as office worker, if not more. And there's little inherent reason to separate "primary school teacher" from teachers at other levels I don't think some jobs are inherently more groupable, I think the choice of grouping is purely arbitrary. We could just as easily have separated long-haul truckers from local delivery people and these charts would completely change.