Will Insistence on Practicing Medicine According to Expected Utility Theory Lead to an Increase in Diagnostic Testing? Reply to DeKay's Commentary: Physicians' Anticipated Regret and Diagnostic Testing

Michael DeKay contends that patients are better off if physicians act based on expected utility theory (EUT). This is, of course, a several decades-old debate. Our article is an attempt to contribute to this debate by providing a descriptive (and not normative) account for some observed decision-making behavior. However, one of our key messages is that not behaving according to the EUT rationality criterion does not make behavior irrational. In the same fashion, consideration of testing from physicians’ point of view, although raising important ethical challenges, may not necessary jeopardize patients’ best interests. It is undeniable fact that physicians do not act according to EUT. Consider an example of treatment and diagnosis of pulmonary embolism (PE) we discussed in our article. According to EUT, if no diagnostic test is taken into consideration, physicians should treat patients with suspected PE as long as probability of pPE > 1.62%. Or, if a spiral computed tomography (CT) scan is available, they should order it for any pPE > 0.07%. No physician, even those of us who are staunch believers in the EUT rationality criterion, does it. Most experts and guidelines panels recommend that PE should be excluded in patients with a probability of PE lower than 5%, the value that is 72 times higher than the EUT threshold of 0.07%! DeKay offers the EUT malpractice liability model as an alternative, arguing that defensive testing (presumably aimed at reducing physicians’ regret about being wrong) harms patients. The model, however, stops short of calculating the exact probabilities of, say, PE, at which DeKay would recommend treating patients with PE or recommend ordering a CT angiogram. Only when one considers actual outcomes (thresholds) can he or she get better appreciation of the usefulness and validity of models. Below, we provide our attempt to illustrate the results of different thresholds at which physicians can be expected to order a diagnostic test according to EUT, EUT-liability, and acceptable regret model. In the accompanying piece, we also provide corrections of our original model as well as further clarifications under which circumstances the acceptable regret model can explain both overtesting and undertesting (when EUT is used as a criterion for diagnostic overand undertesting). We first note that DeKay does, in fact, acknowledge that ‘‘it may be reasonable to ignore small, clinically irrelevant differences between the expectations of treatment options. ’’ What constitutes ‘‘small, clinically irrelevant differences’’ and how to operationalize them is, however, a crucial issue. This is, in fact, the basis of acceptable regret (Ro), which we defined as a loss in utility when undertaking a wrong decision that will not be particularly burdensome to the decision maker. The conceptual advantage of our model is that is derived from regret—that is, one of the basic From the Department of Mathematics, Indiana University Northwest, Gary, Indiana (IH) and University of South Florida, Clinical Translational Science Institute, Center for Evidence-Based Medicine and Health Outcomes, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida (BD).