on the floor wrote:
Not for all of us. I'm an American who out earned you by a significant margin and returned to school for a doctorate in engineering. I simply wanted a career in research. My earnings outlook is a bit better with a PhD as well, but the decision really wasn't a monetary one. To each their own in my opinion.
The answer to the original question depends on university and field of study. It isn't a battle of pure iq in many cases to earn a phd from a directional state school in a weak topic. On the other hand, some of the STEM fields at places like MIT and Stanford have ~25-50% failure rates on their qualifying exams. It's quite difficult to even get admitted to those departments, so the people 'failing' out are not dummies.
I've seen the qualifying exams at a less prestigious (but known for engineering) school, and they were no joke. You'd certainly have to spend months preparing for them, and the professor who designed them prided himself on the fact that >50% of people failed the first time.
On the other hand, my brother is doing a PhD in a science at an Ivy school, and seemed to have a much more relaxed qualifying exam, basically just going over his plans for research.