Relative concave utility for risk and ambiguity

This paper presents a general technique for comparing the concavity of different utility functions when probabilities need not be known. It generalizes: (a) Yaari's comparisons of risk aversion by not requiring identical beliefs; (b) Kreps and Porteus' information-timing preference by not requiring known probabilities; (c) Klibanoff, Marinacci, and Mukerji's smooth ambiguity aversion by not using subjective probabilities (which are not directly observable) and by not committing to (violations of) dynamic decision principles; (d) comparative smooth ambiguity aversion by not requiring identical second-order subjective probabilities. Our technique completely isolates the empirical meaning of utility. It thus sheds new light on the descriptive appropriateness of utility to model risk and ambiguity attitudes. (C) 2012 Elsevier Inc. All rights reserved.