IS EXPECTED UTILITY-THEORY NORMATIVE FOR MEDICAL DECISION-MAKING

Expected utility theory is felt by its proponents to be a normative th eory of decision making under uncertainty. The theory starts with some simple axioms that are held to be rules that any rational person woul d follow. It can be shown that if one adheres to these axioms, a numer ical quantity, generally referred to as utility, can be assigned to ea ch possible outcome, with the preferred course of action being that wh ich has the highest expected utility. One of these axioms, the indepen dence principle, is controversial, and is frequently violated in exper imental situations. Proponents of the theory hold that these violation s are irrational, The independence principle is simply an axiom dictat ing consistency among preferences, in that it dictates that a rational agent should hold a specified preference given another stated prefere nce. When applied to preferences between lotteries, the independence p rinciple can be demonstrated to be a rule that is followed only when p references are formed in a particular way. The logic of expected utili ty theory is that this demonstration proves that preferences should be formed in this way. An alternative interpretation is that this demons trates that the independence principle is not a valid general rule of consistency, but in particular, is a rule that must be followed ii one is to consistently apply the decision rule ''choose the lottery that has the highest expected utility.'' This decision rule must be justifi ed on its own terms as a valid rule of rationality by demonstration th at violation would lead to decisions that conflict with the decision m aker's goals. This rule does not appear to be suitable for medical dec isions because often these are one-time decisions in which expectation , a long-run property of a random variable, would not seem to be appli cable. This is particularly true for those decisions involving a non-t rivial risk of death.