Risk attitude in gambles with years of life: empirical support for prospect theory

According to prospect theory, risk attitude changes depending on whether a prospect is perceived as a gain or a loss relative to a reference or aspiration level. To investigate risk attitude with respect to years of life, the authors elicited utilities at two occasions by the certainty equivalent method from 30 women from the general population. The respondents gave certainty equivalents to gambles with years of life. The gambles were two-outcome gambles with equal probabilities to experience each outcome. A shift from a risk-seeking towards a risk-averse attitude was observed with increasing expected value of the gambles. For each individual, the averaged responses over the two replications were fitted with an s-shaped logistic curve that showed an excellent fit (r2 > or = 0.97) for all respondents. The aspiration level of survival can be derived from this function and was negatively correlated with age (r = -0.43, p < 0.025). The data are consistent with prospect theory and may explain why patients opt for risky treatments, since most of the respondents were risk-seeking in the short term.