Naturally a doctor would have more authority on a subject than some random person, because the experience is a combination of book studies, hands-on studies and years of doing the job.
I'll take his opinion over someone else, so I agree with Ush there.
However, I think what PVS meant was (could be wrong) the kind of person who studies a class for a bit and assumes to be an authority on the subject over someone else. Anyone can study from a book, just because you got taught it doesn't mean you know more than someone who didn't. They could easily know what you know anyway.
Where as I can't say to a doctor, "I've operated on someone.".
-AC