Doctor’s competence

I have a commentary on a nice paper on the accuracy of skin cancer diagnosis coming out in Acta. Opening paragraph below.

Frank Davidoff, the celebrated US physician, has a telling metaphor for medical competence: he likens it to Dark Matter, the material physicists think makes up most of the Universe, and about which we know so little (1). Clinical competence would, in this analogy, be the material that literally holds and binds clinical practice – our professional lives – together. How come we know so little about it?