Séminaire décision, rationalité, interaction : 2014-2015

Décision, rationalité et interaction » est un séminaire mensuel consacré aux sciences de la décision et à l’économie. Il porte aussi bien sur les différentes branches de la théorie du choix rationnel (théorie de la décision, théorie des jeux, théorie du choix social) que sur les questions philosophiques (notamment méthodologiques) soulevées par la science économique.mènent une réflexion sur cet usage.

Responsable (s): 

Séminaire Décision, rationalité, interaction : Philippe Mongin

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Thursday 2 October 2014 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Philippe Mongin (CNRS, GREG-HEC) interviendra sur le sujet "Les préférences étendues, les comparaisons interpersonnelles et l'identité de l'agent économique".

Séminaire Décision, rationalité, interaction : Ivan Moscati

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Thursday 13 November 2014 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Nous aurons le plaisir d'entendre un exposé d'Ivan Moscati (Università degli Studi dell'Insubria) intitulé : "The Debate on the Measurability of von Neumann and Morgenstern's Utility Function, 1944-1954".

Séminaire Décision, rationalité, interaction : Jean-Christophe Vergnaud

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Thursday 11 December 2014 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Nous aurons le plaisir d'entendre un exposé de Jean-Christophe Vergnaud (CNRS, Université Paris-I).

Séminaire décision, rationalité, interaction : Orri Stefansson

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Thursday 22 January 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Nous aurons le plaisir d'entendre un exposé d'Orri Stefansson (Collège d'Études Mondiales), intitulé : "How Should We Evaluate Chances?".

Résumé : It is standardly assumed that chances are not carriers of value, but are only instrumentally valuable in virtue of the outcomes with which they are associated. Learning that you have won a lottery, and that your chances of winning were, say, 0.000001, is on this view neither more nor less desirable than just learning that you have won the lottery. I call this view—implicitly assumed, for instance, in expected utility theory, risk analysis and orthodox economics---Chance Neutrality. The aim of this paper is to question the claim that Chance Neutrality is rationally required. I will do so by first showing that given Chance Neutrality, the Principal Principle---according to which a person should align her credence with her beliefs about objective chance---entails Linearity---the idea that the value of a lottery is equal to the sum of the values of the lottery’s prizes discounted by their probabilities. I then argue that the Principal Principle is a requirement of (both practical and theoretical) rationality but that Linearity is not. Hence, Chance Neutrality is not rationally required. I conclude with some remarks on implications for the Ellsberg paradox. 
 

Séminaire décision, rationalité, interaction : Marcus Pivato

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Thursday 5 February 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Marcus Pivato (THEMA, Université de Cergy-Pontoise) interviendra sur le sujet : ''Bayesian Social Aggregation: Beyond Ex Ante and Ex Post."

Suppose a society must make policy choices while facing uncertainty about the outcome of these choices. Each policy determines a social prospect, which will yield a payo for each individual, but these payos depends upon the (unknown) state of nature. The problem is how to choose the best social prospect, given uncertainty about the true state of nature. The first major result in this area was Harsanyi's Social Aggregation Theorem. This theorem (and its generalizations) begins with two premises: (1) all individuals (and society as a whole) are rational agents, and (2) the decisions of society should conform to the ex ante Pareto axiom, which says that, if everyone prefers prospect X over prospect Y, then society should also prefer prospect X over prospect Y . From these two premises, Harsanyi deduces that society should seek to maximize the expected value of a utilitarian social welfare function. However, existing versions of Harsanyi's theorem suer from three shortcomings:

  1. They assume that all agents can formulate preferences over all possible social prospects, even those which are infeasible or logically absurd.
  2. They assume that all agents are subjective expected utility (SEU) maximizers |i.e. each agent seeks to maximize the expected value of her utility function with respect to her probabilistic beliefs.
  3. They imply that all agents must have the same probabilistic beliefs. Given the doxastic heterogeneity we observe in the real world, this is generally regarded as a reductio ad absurdum of the whole approach.

We relax the SEU assumption by only requiring the individuals and the society to satisfy the Statewise Dominance axiom, which is arguably the bare minimum requirement for rationality. Furthermore, we relax the \universal domain" assumption, by only requiring agents' preferences to be dened on an open, connected set of social prospects. From these weaker hypotheses, we still obtain the conclusions of Harsanyi's theorem; SEU-maximization appears as a conclusion of our theorem, not a hypothesis.

Unfortunately, this still yields the aforementioned agreement in probabilistic beliefs. To resolve this, we introduce two independent sources of uncertainty: one objective, and one subjective. In this framework, we obtain a version of the Social Aggregation Theorem that is compatible with diversity in beliefs. In our result, ex ante social preferences still maximize expected value of a utilitarian social welfare function, and all agents must have the same beliefs about the objective uncertainty source. But they can have dierent beliefs about the subjective uncertainty source.

En fichier attaché, vous trouverez l'article qui servira d'arrière-plan à l'exposé.

 

Séminaire décision, rationalité, interaction : Olivier Roy

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Thursday 5 March 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Olivier Roy (University of Bayreuth)

Séminaire décision, rationalité, interaction : Raphaël Giraud

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Thursday 2 April 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Raphaël Giraud (LED, Université Paris-VIII) interviendra sur le sujet  "An Elementary Axiomatization of the Smooth Ambiguity Model".

Résumé : The smooth ambiguity model (Klibanoff, Marinacci, and Mukerji, 2005) is a growingly popular model of decision making under ambiguity among applied economists because it is very tractable compared to other alternatives. As far as its preference foundations are concerned, however, the situation is not entirely satisfactory: axiomatizations exist in the literature (Klibanoff et al., 2005; Nau, 2006; Seo, 2009; Giraud, 2014), yet none of them is set up in a framework that would make it directly comparable to the axiomatizations of alternative models. All extant axiomatizations use some form of enriched setup with respect to the traditional setup involving only first order acts (Savage acts or Anscombe-Aumann horse lotteries), they are not elementary. By contrast, we aim here at providing an elementary axiomatization of SOSEU, in the sense of only using first order acts. We show that the main axiom characterizing SOSEU in the class of preferences satisfying both continuity and the separation of utility from beliefs is a form of probability-wise dominance axiom with a twist capturing ambiguity attitude: given two portfolios of acts (i.e. weighted combinations of acts), if the weighted average of ambiguity-twisted expectations of each act in the first portfolio is larger than the corresponding weighted average of the second portfolio for all possible priors, then replacing the expectation by the certainty equivalent for each act in the portfolio does not reverse the preference. We also examine to what extent our axiomatization can be seen as a reduced form of other axiomatizations in the literature and prove that not all axiomatizations are equivalent, in the sense that Seo (2009)’s axiomatization uses the same amount of information as the one contained in our axiomatization, whereas Klibanoff et al. (2005)’s framework and axiomatization use extra and irreducible information. 

Séminaire décision, rationalité, interaction : Gabriella Pigozzi

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Thursday 16 April 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Gabriella Pigozzi (LAMSADE, Université Paris-Dauphine)

Séminaire décision, rationalité, interaction : Conrad Heilmann

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Thursday 7 May 2015 - 17:00 to 19:00
Département d'Études Cognitives de l'École Normale Supérieure - 29 rue d'Ulm 75005 Paris

Conrad Heilmann (Erasmus University, Rotterdam)