Incomplete preferences and confidence

A theory of incomplete preferences under uncertainty is proposed, according to which a decision maker’s preferences are indeterminate if and only if her confidence in the relevant beliefs does not match up to the stakes involved in the decision. We use the representation of confidence in beliefs introduced in Hill (2013), and axiomatise a class of models, differing from each other in the appropriate notion of stakes. The theory naturally suggests two distinct strategies for completing preferences, and hence for choosing in the presence of incompleteness: one that relies only on beliefs in which the decision maker is sufficiently confident, and one that mobilises all beliefs, no matter how little confidence she may have in them. Axiomatic characterisations are given for completion procedures following each of the strategies. Finally, in a market setting, the incorporation of confidence is shown to add an extra friction, beyond the standard implications of non-expected utility models for Pareto optima.