An interesting statement I've seen in a couple of books about IQ testing as an employment qualification is that at ALL levels of ability it is advantageous to seek a college degree if that degree makes the difference between being classified as an "engineer" rather than being classified as a "technician." Some technicians plainly are very smart and very economically useful to the organizations that employ them. Both technicians and engineers can be found at a variety of levels of ability. But for the individual job-seeker, whatever the level of ability, the expedient thing to do (in that category of occupations) is seek the college degree and become an engineer. Apparently, the job market treats even a lousy engineer who is barely able to do engineering work better than a technician who is matched by ability proxy (IQ score) before the degree was sought.

I offer no firm conclusion about why this is so. Perhaps engineering programs in colleges impart skills that are valued by the job market enough to boost an engineer's earnings over the long term. Or perhaps hiring and promotion procedures in many companies favor the social signal given by possessing a college degree. Or perhaps there is a lurking variable other than IQ that distinguishes persons who seek engineering degrees from persons who do not seek engineering degrees for technical occupations. It would take more data to tease out the causation of this phenomenon reported in the literature on job-candidate testing for employment, but meanwhile I would advise people near and dear to me who have such career aspirations to seek an engineering degree if at all possible, as that appears to offer positive economic returns for a person with a typical lifespan and labor force participation.

I have no comment on the usefulness of degrees in other subjects, which may vary quite a lot.