JOSÉ HELENO FARO

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  • Artigo Científico
    Dynamically consistent objective and subjective rationality
    (2022) Bastianello, Lorenzo; JOSÉ HELENO FARO; Santos, Ana
    A group of experts, for instance climate scientists, is to advise a decision maker about the choice between two policies f and g. Consider the following decision rule. If all experts agree that the expected utility of f is higher than the expected utility of g, the unanimity rule applies, and f is chosen. Otherwise, the precautionary principle is implemented and the policy yielding the highest minimal expected utility is chosen. This decision rule may lead to time inconsistencies when adding an intermediate period of partial resolution of uncertainty. We show how to coherently reassess the initial set of experts’ beliefs so that precautionary choices become dynamically consistent: new beliefs should be added until one obtains the smallest “rectangular set” that contains the original one. Our analysis offers a novel behavioral characterization of rectangularity and a prescriptive way to aggregate opinions in order to avoid sure regret.
  • Artigo Científico
    Ambiguity through confidence functions
    (2009) Chateauneuf, Alain; JOSÉ HELENO FARO
    We characterize preference relations over bounded below Anscombe and Aumann’s acts and give necessary and sufficient conditions that guarantee the existence of a utility function u on consequences, a confidence function ϕ on the set of all probabilities over states of nature, and a positive threshold level of confidence ˛0 such that our preference relation has a functional representation J, where given an act f J(f) = min p ∈ L˛0 ϕ 1 ϕ(p) S u(f) dp. The level set L˛0ϕ := {p : ϕ(p) ≥ ˛0} reflects the priors held by the decision maker and the valueϕ(p) captures the relevance of prior p for his decision. The combination ofϕ and˛0 may describe the decision maker’s subjective assessment of available information. An important feature of our representation is the characterization of the maximal confidence function which allows us to obtain results on comparative ambiguity aversion and on special cases, namely the subjective expected utility, the Choquet expected utility with convex capacity, and the maxmin expected utilit