Fabio Maccheroni

Differentiating ambiguity and ambiguity attitude

Abstract The objective of this paper is to show how ambiguity, and a decision maker (DM)s response to it, can be modelled formally in the context of a general decision model. We introduce a relation derived from the DMs preferences, called “unambiguous preference”, and show that it can be represented by a set of probabilities. We provide such set with a simple differential characterization, and argue that it is a behavioral representation of the “ambiguity” that the DM may perceive. Given such revealed ambiguity, we provide a representation of ambiguity attitudes. We also characterize axiomatically a special case of our decision model, the “ α -maxmin” expected utility model.

A strong law of large numbers for capacities

We consider a totally monotone capacity on a Polish space and a sequence of bounded p.i.i.d. random variables. We show that, on a full set, any cluster point of empirical averages lies between the lower and the upper Choquet integrals of the random variables, provided either the random variables or the capacity are continuous.

Dynamic variational preferences

We introduce and axiomatize dynamic variational preferences, the dynamic version of the variational preferences we axiomatized in [F. Maccheroni, M. Marinacci, A. Rustichini, Ambiguity aversion, robustness, and the variational representation of preferences, Mimeo, 2004], which generalize the multiple priors preferences of Gilboa and Schmeidler [Maxmin expected utility with a non-unique prior, J. Math. Econ. 18 (1989) 141–153], and include the Multiplier Preferences inspired by robust control and first used in macroeconomics by Hansen and Sargent (see [L.P. Hansen, T.J. Sargent, Robust control and model uncertainty, Amer. Econ. Rev. 91 (2001) 60–66]), as well as the classic Mean Variance Preferences of Markovitz and Tobin. We provide a condition that makes dynamic variational preferences time consistent, and their representation recursive. This gives them the analytical tractability needed in macroeconomic and financial applications. A corollary of our results is that Multiplier Preferences are time consistent, but Mean Variance Preferences are not.

Revealed Ambiguity and Its Consequences: Updating

We study the updating of beliefs under ambiguity for invariant biseparable preferences. In particular, we show that a natural form of dynamic consistency characterizes the Bayesian updating of these beliefs.

Certainty Independence and the Separation of Utility and Beliefs

Economists often operate under an implicit assumption that the tastes of a decision maker are constant, while his beliefs change with the availability of new information. It is therefore customary to seek representations of preferences which cleanly separate the taste component, called ‘utility,’ from the beliefs component. We show that a complete separation of utility from the other components of the representation is possible only if the decision maker’s preferences satisfy a mild but not completely innocuous condition, called ‘certainty independence.’ We prove that the preferences that obtain such separation are a subset of the biseparable preferences.nonatomic probability measures, we extend some of these results to the case of individuals with decreasing marginal evaluations.

How to cut a pizza fairly: Fair division with decreasing marginal evaluations

Abstract. Existential and constructive solutions to the classic problems of fair division are known for individuals with constant marginal evaluations. By considering nonatomic concave capacities instead of nonatomic probability measures, we extend some of these results to the case of individuals with decreasing marginal evaluations.

Coherence without additivity

The Dutch book argument is a coherence condition for the existence of subjective probabilities. This paper gives a general framework of analysis for this argument in a nonadditive probability setting. Particular cases are given by comonotonic and affinely related Dutch books that lead to Choquet expectation and Min expectations.

Ambiguity and robust statistics

Starting with the seminal paper of Gilboa and Schmeidler (1989) [32] an analogy between the maxmin approach of decision theory under ambiguity and the minimax approach of robust statistics – e.g., Blum and Rosenblatt (1967) [10] – has been hinted at. The present paper formally clarifies this relation by showing the conditions under which the two approaches are actually equivalent.

Insurance Premia Consistent with the Market

We consider insurance prices in presence of an incomplete and competitive market. We show that if the insurance price system is internal, sublinear, and consistent with the market, then insurance prices are the maxima of their expected payments with respect to a family of risk neutral probabilities. We also show that under a simple additional assumption it is possible to decompose the obtained price in net premium plus safety loading.

Classical subjective expected utility

We consider decision makers who know that payoff-relevant observations are generated by a process that belongs to a given class M, as postulated in Wald [Wald A (1950) Statistical Decision Functions (Wiley, New York)]. We incorporate this Waldean piece of objective information within an otherwise subjective setting à la Savage [Savage LJ (1954) The Foundations of Statistics (Wiley, New York)] and show that this leads to a two-stage subjective expected utility model that accounts for both state and model uncertainty.