It seems to me that the problem with the "librarian / salesperson" example is that the term "shy" is not clearly defined. How shy? Does the person feel slightly uncomfortable speaking to unfamiliar people, or is it so severe that they start blushing, sweating and possibly stammering? How shy can a person be and still get a job as a salesperson? When does it become an exclusionary criteria, rendering the base rate irrelevant? So, for example, if you meet a new person and all you know about them is that they speak just one language, are they more likely to be a translator/interpreter or a pediatric surgeon? Well, obviously, the correct answer is translator/interpreter, since there are seventy times as many translators/interpreters in the United States than pediatric surgeons. Right? Or not? Hmmm... :-)