Eric Danan

Randomization vs. Selection: How to Choose in the Absence of Preference?

Decision makers sometimes have to choose between alternative options about which they have no preference: either they judge the options equally valuable (indifference) or they have no judgment about their relative value (noncomparability). Choosing randomly is generally considered a natural way to deal with such situations. This paper shows, however, that systematic randomization between noncomparable options may lead to a chain of decisions resulting in monetary losses (a money pump). Furthermore, these losses can be avoided by deliberately selecting one of the noncomparable options instead of randomizing. Thus, randomization among noncomparable options is costly relative to deliberate selection. On the other hand, randomization among indifferent options is costless relative to deliberate selection.

Revealed preference and indifferent selection

It is shown that preferences can be constructed from observed choice behavior in a way that is robust to indifferent selection (i.e., the agent is indifferent between two alternatives but, nevertheless, is only observed selecting one of them). More precisely, a suggestion by Savage (1954) to reveal indifferent selection by considering small monetary perturbations of alternatives is formalized and generalized to a purely topological framework: references over an arbitrary topological space can be uniquely derived from observed behavior under the assumptions that they are continuous and nonsatiated and that a strictly preferred alternative is always chosen, and indifferent selection is then characterized by discontinuity in choice behavior. Two particular cases are then analyzed: monotonic preferences over a partially ordered set, and preferences representable by a continuous pseudo-utility function.

Aggregating Tastes, Beliefs, and Attitudes Under Uncertainty

The authors provide possibility results on the aggregation of beliefs and tastes for Monotone, Bernoullian and Archimedian preferences of Cerreia-Vioglio, Ghirardato, Maccheroni, Marinacci, and Siniscalchi (2011). The authors propose a new axiom, Unambiguous Pareto Dominance, which requires that if the unambiguous part of individuals’ preferences over a pair of acts agree, then society should follow them. They characterize the resulting social preferences and show that it is enough that individuals share a prior to allow non dictatorial aggregation. A further weakening of this axiom on common-taste acts, where cardinal preferences are identical, is also characterized. It gives rise to a set of relevant priors at the social level that can be any subset of the convex hull of the individuals’ sets of relevant priors. The authors then apply these general results to the Maxmin Expected Utility model, the Choquet Expected Utility model and the Smooth Ambiguity model. They end with a characterization of the aggregation of ambiguity attitudes.