If a decision maker, in a world of uncertainty à la Anscombe and Aumann (1963), can choose acts according to some objective probability distribution (by throwing dice for instance) from any given set of acts, then there is no set of acts that allows an experimenter to test more than the Axiom...

A decision maker (DM) is asked to make choices from a set of acts, which entail both risk and uncertainty in the sense of knight (1921). Extending Raiffa's (1961) argument I show that, provided the DM can choose acts objectively randomly (by flipping her own fair coin, for instance), provided...

I study the implications of Abraham Wald's (1947) complete class theorem for decision making under Knightian uncertainty (or ambiguity). Suppose we call someone who uses Wald's approach to statistical decision making a Waldian. A Waldian may then have preferences over acts that are not in...

Ambiguity averse decision-makers can behave in financial portfolio problems in ways that cannot be rationalized as subjective expected utility maximization. Indeed, [Dow and da Costa Werlang, Econometrica 1992] show that an ambiguity-averse decision-maker might abstain from trading an asset for...