The analysis of medical practice as a decision-making process underscores the proposition that the choice of a therapy should reflect not only the knowledge and experience of the physician but also the values and the attitudes of the patient (McNeil, Weischselbaum, and Pauker, 1981). But if patients are to play an active role in medical decision making – beyond passive informed consent – we must find methods for presenting patients with the relevant data and devise procedures for eliciting their preferences among the available treatments. However, the elicitation of preferences, for both patients and physicians, presents a more serious problem than one might expect. Recent studies of judgment and choice have demonstrated that intuitive evaluations of probabilistic data are prone to widespread biases (Kahneman, Slovic, and Tversky, 1982), and that the preference between options is readily influenced by the formulation of the problem (Tversky and Kahneman, 1986).

In a public health problem concerning the response to an epidemic, for example, people prefer a risk-averse strategy when the outcomes are framed in terms of the number of lives saved and a risk-seeking strategy when the same outcomes are framed in terms of the number of lives lost. The tendency to make risk-averse choices in the domain of gains and risk-seeking choices in the domain of losses is a pervasive phenomenon that is attributable to an S-shaped value (or utility) function, with an inflection at one's reference point (Kahneman and Tversky, 1979, 1984).