Abstract
When the presence of a specific disease is being considered, a diagnostic test can often help the physician to choose between subjecting the patient to an extensive workup (or treatment) and proceeding no further. Decisions concerning the use of a test require that three judgments be made: (1) Should the test be done? (2) Which test (if any) should be used if two or more are available? (3) If a test that can take on more than two values is performed, what is the correct cutoff point (or positivity cri terion) that determines whether or not to proceed? This paper presents a mathemati cal technique to answer these questions, taking into account data concerning the patient (summarized as the prior, or pre-test, probability of disease), the test, and the workup (or treatment). The technique is presented in a graphical form that can be applied to any clinical situation in which the needed data are available. (Med Decis Making 3:177-195, 1983)