Question normal

I live in Japan where cases of medical negligence are much fewer than in the U.S. I have heard, however, that while there may be many claims in the U.S., the great majority are decided in favor of the physician. My question concerns the 'reasonable person doctrine' used to decide cases of medical negligence. When considering a 'misdiagnosis' as opposed to a 'mistake', can the reasonable person doctrine be used to decide a case where cognition, rather than reasonable practice is the issue - or are they the same thing?