Eliciting Health State Utilities Using Paired-Gamble Methods: The Role of the Starting Point

Paired-gamble methods have been proposed to avoid the "certainty effect" associated with standard gamble methods.

This study examines the role of starting-point effects in paired-gamble methods. In particular, it examines how the utilities so derived vary as a function of the probabilities of the stimulus lottery.

A sample of 455 members of the Spanish general population valued 9 health states via face-to-face interviews. Subjects were randomly placed into 3 subgroups, which differed in terms of the stimulus gamble's probability. Nonparametric tests and an interval regression model were used to test if utilities change when the probability distribution is modified.

Nonparametric tests showed that the probability of a health state being considered worse than death did not differ among subgroups. Nevertheless, changes in the stimulus gamble did produce significant differences in the distribution of utilities: the higher the probability of full health in the stimulus, the higher the utility elicited. Regression estimates support the existence of starting-point effects when the utilities are obtained under expected utility. According to the prospect theory, the conclusions depend on the reference point considered. When the reference points used are death or the health state evaluated, we observe differences among these groups. Nevertheless, when full health is used, these differences disappear.

This research suggests that paired-gamble methods may also be susceptible to starting-point effects. Yet the differences are small, and they disappear when the data are analyzed using prospect theory with full health as the reference point.