Clinical decision making is the process by which we determine who needs what, when. While not exactly arbitrary, this exercise can be quite subjective. Each clinician compiles their own data (hence the emphasis on learning to perform an accurate H&P) and then constructs an argument for a particular disease state based on their interpretation of the "facts." The strength of their case will depend on the way in which they gather and assemble information. There may then be no single, right way of applying diagnostic and therapeutic strategies to a particular case. Of course, not every situation is a clinical quandary. A patient with a known history of coronary artery disease presenting with 3 hours of crushing chest pain, an EKG with 4mm ST segment elevations across the precordial leads, and an initial Troponin-I of 50 is having a myocardial infarction. That is a diagnostic slam dunk. More commonly, however, there exist elements of uncertainty. Medicine involves playing the odds, assessing the relative chance that a patient is/is not suffering from a particular illness. Codifying the way in which clinicians logically approach problems and deal with this uncertainty is a difficult task.