Séminaires passés


Arianna Novaro - Université Paris I

Mardi 30 novembre 2021 - 11 h / 12 h
Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desplas

Abstract :
There are numerous examples of situations where a group of agents need to find a collective interval based on their individual preferences: think for instance of a committee having to agree on a time slot for a meeting, that is asked to express their preferences over a starting/ending time (or on a starting time and a duration). In this talk I will present ongoing work about the impact that the choice of representation for the intervals has on their aggregation. 
Specifically, I will show that on discrete scales we cannot have natural rules that can be defined both as rules that aggregate separately the left and right endpoints of intervals and as rules that aggregate separately the left endpoints and the interval widths; however, on continuous scales such rules correspond to the weighted averages of the endpoints of the individual intervals.

This is joint work with Ulle Endriss (ILLC, University of Amsterdam) and Zoi Terzopoulou (LAMSADE, University of Paris Dauphine).


Alessandra Pizzo - Université Paris VIII

(avec Benjamin Villena - Universidad Diego Portales, Chili)

Mardi 23 novembre 2021  - 11 h / 12 h
Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desplas

Abstract :
Labor markets reward the most talented workers through high wages and beneficial transitions, and the opposite occurs for the most unproductive ones. These casual observations relating worker flows and ability or match quality find empirical support: the unemployment rate and wage inequality have highly significant, positive and concave relation over time and across states in the US. Job finding rates and Job-to-job transitions also share this common pattern. We rationalize these facts through employer hiring selectivity in a non-sequential search model with on-the-job search. Most qualified applicants, either unemployed or employed, have higher chances to be hired, especially when unemployment is high. Employer selectivity also generates a general equilibrium composition effect affecting inequality. We estimate our model using CPS worker flows and wages data via Generalized Method of Moments. We explain part of the positive and concave relation between unemployment and wage inequality by shifts in the average worker/match productivity.


Eric Danan - Université Cergy-Pontoise

Mardi 16 novembre 2021 - 11 h / 12 h
Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desplas

Abstract :
Mongin (1994) proved a multi-profile version of Harsanyi (1955)'s Aggregation Theorem: within the expected utility model, a social welfare functional mapping profiles of individual utility functions into social preference relations satisfies the Pareto and Independence of Irrelevant Alternatives principles if and only if it is utilitarian. The present paper extends Mongin's analysis by allowing individuals to have incomplete preferences, represented by sets of utility functions. An impossibility theorem is first established: social preferences cannot satisfy all the expected utility axioms, precluding utilitarian aggregation in this extended setting. Adapting the objective vs. subjective rationality approach of Gilboa et al. (2010) to the present social choice settings representation theorems are then obtained by relaxing either the Completeness or the Independence axioms at the social level, yielding two forms of partial utilitarianism.

Lien vers l'article.


Philippe Bich - Université Paris I

Mardi 26 octobre 2021-11 h / 12 h
Lemma - 4 rue Blaise Desgoffe, 75006 Paris. Salle Maurice Desgoffe


In this paper, we axiomatize the maxmin version of the quasi-hyperbolic model I(x)= min {p0x0 +(1−p0)(1−δ)x1 +(1−p0)(1−δ)δx2 +(1−p0)(1−δ)δ2x3…}, where (x0, . . . , xn, . . . ) is a deterministic consumption stream, the minimum being taken on the set of all present bias parameters p0 and discount rates δ in some given set Q. When there is no present bias, we recover Chambers and Echenique’s axiomatization of maxmin exponential preferences (ECMA 2018), and when there is no ambiguity on the set of discount rates and present bias parameters (i.e. when Q is a singleton), we get Montiel Olea and Strzalecki’s axiomatization of quasi-hyperbolic preferences (The Quarterly Journal of Economics 2014). To prove our main result, we provide some intertemporal variational representation results of interest for its own sake.

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