In medical decision making, a utility is a measure of the relative desirability that a person attributes to a particular health state, under conditions of risk. Two points are noteworthy here.

First, a utility is a relative measure. A person's utility for the health state of interest—the target health state—is revealed by comparing it with two extreme health states. One extreme is preidentified as highly undesirable and arbitrarily ascribed a utility of 0.00. The other extreme is preidentified as highly desirable and arbitrarily ascribed a utility of 1.00. Unless the person considers the target health state to be preferentially equivalent to either extreme, his utility for that state falls somewhere between 0.00 and 1.00.

Second, a utility is measured under conditions of risk. The assessment process involves ...