The study accounted for people in any career who had only a BA in philosophy and no graduate degree. It did the same for other jobs, so if you had an civil engineering degree but worked as a business consultant, your salary would still be counted in the civil engineering category. And if you had say a BA in philosophy but worked as a lawyer because you also had a JD, you wouldn't be counted. They followed somewhere around a million people, but I don't know the specifics of the study parameters.
I think it would be very hard to account for people who stayed in philosophy only jobs because what would you count outside of academia? I personally would say that it's easy to argue that most legal or government policy jobs should count, but you could make an argument for almost any field on the basis of studying logic and ethics alone.
Business and medical ethics are two areas that I have seen brought up for careers where a background in philosophy is useful, but I wouldn't consider business management or health administration to be in a "philosophy sector" for example. Same with studying logic and going on to become a software engineer, which is brought up pretty frequently as well as a career area where philosophy majors seem to do well.
I don't think the goal of most philosophy majors is to pull a Thoreau and get metaphysical in the woods, which is what I think most people sort of picture them doing. For most people in the major, I don't think being a business consultant is really a consolation prize because they couldn't find work as a philosopher.
It also bears saying that the worst earners with a BA in philosophy are probably doing significantly worse than someone with a BA in something like nursing, and their entry level salaries are very low on average. There's a lot more variability among philosophy earners than many STEM careers, probably because they're all over the map in different fields. So my point is definitely not "Go be a Philosophy Major instead of a doctor! You'll definitely make all the Money!" because that would be terrible life advice. (Let's be honest, we all should have been engineers if we wanted that sweet debt:income ratio.)
For the few people who asked something like "but what would you
do with a philosophy degree???", If I remember correctly, the places philosophy majors went from my school were mostly:
graduate school (law school or PhD)
legal research / paralegal (often a stepping stone for law school)
business / business consulting
Wall Street / finance
government (mostly federal)
journalism
software engineering
Take that list with a grain of salt because 1. that was my specific fancy-pants school and I can't speak to the average philosophy major nationwide and 2. that's based on 15 year old memories and probably some stereotyping that I've decided are memories.
Anecdotally, all of the philosophy majors I know headed to some type of graduate school. The four people I can think of that were my year or the year above obtained a JD, a joint MD/MA in bioethics, a PhD in philosophy, and a PhD in history (with some specialization related to ethics in his work, and I think a stint as a freelance journalist before graduate school). They work respectively as a lawyer, a doctor, and as professors. So only one is actually a philosopher, but I'd argue that all four are working in some type of philosophical capacity.
PS - Sorry for derailing the thread. As a humanities major I get very defensive when I feel like the humanities are getting piled on as somehow being unworthy of study or incapable of producing a viable career.
My career before vet school was stable, had a lot of potential for growth, and my max career salary probably would have been about the same as it will be after I graduate with a DVM. The main differences are it would have probably taken me longer to hit career max, I would have hated my life for 30 years, and there is a high probability that I would have rage-quit before retirement and gone to live in a yurt.