To demonstrate, let’s look at two dental practices. John serves a population of patients in a poor part of town where most of the citizens don’t have insurance and don’t go to the dentist until their teeth are failing. Ben’s practice, on the other hand, is in a part of town where the patient population is wealthy. Ben’s patients see him every six months, and, thus, have healthy teeth. The state in which these two dentists practice decided to rate dentists based upon the dental hygiene scores of their patients, how often patients go to their dentists, and other variables related to dental outcomes of their patients. Dentist John receives a low score of “1” because of his patient population, not his dental skills. In fact, John is an excellent dentist because he has to take care of dental issues that his friend Ben hardly ever has to deal with. Ben receives a score of “5” because his patients have good dental hygiene and go to the dentist every six months. Ben isn’t the best dentist in the world, but given his healthy dental population, he doesn’t need to be. In fact, Ben refers his more difficult patients to John, who has more experience with difficult cases.