That chart bears out, IMHO, the situations seen anecdotally.
Tech - you can do about the same in your field as opposed to any other high-tech job, i.e., the “going rate” is the “going rate” for a person with your skills. It shows a fluid marketplace. If you are working in a non-tech job, however, bingo ! you make less, because you’re now NOT being thought of as your tech-specialty. Fer example, if you switch from developing websites over to marketing, or customer service.
Math - right now “big data” for business and very much the gubmint is paying BIG for math people. In order to do this work one needs “higher math” skills, which most people simply do not have the brains to do. Mind you, most of the is going in goofy directions, but if it’s paying a lot, you’ll find willing employees. Advanced math degrees can qualify one to work in other high-tech fields. But right away we see a hit in pay, because the jobs are not so in-demand, and... you’re lumped into a job field that’s loaded with other people looking for work - and no advanced math degree is required for those jobs. Non-tech - same situation, but even moreso.
Engineering - people see a decent job market for their specialty (big corps would LOVE to flood this market with cheap labor). And, if you change specialties - you’re probably still doing something very technical, and you only made the switch because you could earn more. Engineering degree - and the work itself - requires a fair amount of smarts, so as much as big corps try to flood the market - trouble is, when they flood the market with stoopid people, even though they have the degree, they’re just not that effective at doing the jobs. Poor little corporate just has to pay up for decent engineers and dey don’t wike it.
Science - more esoteric field that engineering, and even math. It’s dang difficult to get the degree and to do the work. But big corps don’t need so many of these. Jobs where you actually work at science, as opposed to engineering, well, there’s not so many jobs. The degrees can be used to get into other high-tech fields - and undoubtedly it’s usually done to EARN MORE. If one switches to non-tech field... of course, you’re now competing with all non-tech people for those jobs, so you’re not going to earn as much as you could in a tech field.
IMHO, it’s pretty much what one would expect.