Case-Based Expected Utility: Preferences over Actions and

We consider a decision-situation in which the available information is given by a data-set. The decision-maker can express preferences over data-set-action pairs. In particular, he can compare different actions given the available information contained in a data-set and also different data-sets w.r.t. to the evidence they give in support of the choice of a given action. Three characteristics of a data-set can be used to evaluate the evidence it provides with respect to the payoff of a given action: the frequency of observations, the number of observations and the rele-vance of observations to the action under consideration. We state axioms, which ensure that the decision maker is indifferent among data-sets with identical fre-quencies, but different lengths. We then provide an expected utility representation of preferences, in which the beliefs of the decision maker about the outcome of a given action can be expressed as similarity-weighted frequencies of observed cases, as in BGSS (2005). The similarity weights reect the subjectively per-ceived relevance of observations for the specic action