Decision making is the physician's major activity. Every day, in doctors' offices throughout the world, patients describe their symptoms and com- plaints while doctors perform examinations, order tests, and, on the basis of these data, decide what is wrong and what should be done. Although the process may appear routine-even to the physicians in- volved-each step in the sequence requires skilled clinical judgment. Physicians must decide: which symptoms are important, whether any laboratory tests should be done, how the various items of clinical data should be combined, and, finally, which of...