4月8日(火): 16:00-18:30 富士見校舎5階503教室

16:00-17:10

発表者1: 加藤晋 (東京大学社会科学研究所)

タイトル：Population ethics with thresholds (joint work with Walter Bossert and Kohei Kamaga)

概要：We propose a new class of social quasi-orderings in a variable-population setting.  In order to declare one utility distribution at least as good as another, the critical-level utilitarian value of the former must reach or surpass the value of the latter.  For each possible absolute value of the difference between the population sizes of two distributions to be compared, we specify a non-negative threshold level and a threshold inequality.  This inequality indicates whether the corresponding threshold level must be reached or surpassed in the requisite comparison.  All of these threshold critical-level utilitarian quasi-orderings perform same-number comparisons by means of the utilitarian criterion.  In addition to this entire class of quasi-orderings, we axiomatize two important subclasses.  The members of the first subclass are associated with proportional threshold functions, and the well-known critical-band utilitarian quasi-orderings are included in this subclass.  The quasi-orderings in the second subclass employ constant threshold functions; the members of this second class have, to the best of our knowledge, not been examined so far.  Furthermore, we characterize the members of our class that (i) avoid the repugnant conclusion; (ii) avoid the sadistic conclusions; and (iii) respect the mere-addition principle.

17:20-18:30

発表者2: Elena Molis (Universidad de Granada)

タイトル：Group threshold when making a decision (joint work with M. Gomez-Rua and B. Moreno)

概要：We address the problem of making a binary decision under two possible states of the world, where each decision is correct in one of the states. We assume that every agent in a society or group has preferences regarding the different state-decision pairs, which shape their initial inclination towards one of the decisions before receiving any information about the actual state. This inclination can be formalized as a threshold we refer to as bias. The goal of this paper is to provide micro-foundations for how social bias is formed and how it determines the final collective decision. First, we present a direct method for aggregating individual biases using Bias Aggregation Rules. We characterize the family of rules that satisfy anonymity, unanimity, monotonicity, and error asymmetry. Second, we explore an indirect method of aggregation, using a Social Welfare Function that derives a social utility function from individual utility functions over the state-decision pairs. We characterize the functions that satisfy weak Pareto efficiency, neutrality, anonymity, independence of irrelevant alternatives, and monotonicity. Finally, we examine the conditions under which these two aggregating methods of aggregating individual biases are equivalent and yield the same collective decision.

5月13日(火): 16:20-17:50 富士見校舎5階404教室

発表者: 清水木楠 (東京大学大学院経済学研究科博士課程)

タイトル: Value of Information in Social Learning (joint work with Hiroto Sato)

概要: This study extends Blackwell’s (1953) comparison of information to a sequential social learning model in which agents make decisions sequentially based on both private signals and observed actions of others. In this context, we introduce a new binary relation over information structures: an information structure is more socially valuable than another if it yields higher expected payoffs for all agents, regardless of their preferences. First, we establish that this binary relation is strictly stronger than the Blackwell order. Next, we provide a necessary and sufficient condition for our binary relation and propose a simpler sufficient condition that is easier to verify.

6月3日(火): 16:20-18:40 富士見校舎4階404教室

16:20-17:25

発表者1: 野口真平 (一橋大学大学院経済学研究科博士課程)

タイトル: The Value of Experts in Organizations (joint work with Masanori Hatada)

概要: We study contracts that commission experts to collect information. To analyze the value of experts in organizations, we introduce two types of experts: internal experts and external experts. The principal can observe the outcomes of internal  experts’ investigation, but cannot observe those of external experts. The principal  design a contract to ensure that the experts have incentives to  make effort for the  investigation and report the outcomes honestly. In the model with two experts, we first show that to design a contract that induces truthful reporting and effort in a unique equilibrium, engaging an internal expert in investigation is indispensable.  Then, we consider a model with one internal expert and one external expert and  derive a contract that achieves the lowest expected total rewards among contracts  that induces truthful reporting and effort in a unique equilibrium

17:35-18:40

発表者2: 柳田翔平 (一橋大学大学院経済学研究科博士課程)

タイトル: Costly Bayesian Optimism

概要: Individuals often deviate from Bayesian updating by processing information optimistically. In this type of information processing, individuals tend to selectively incorporate information that is favorable to them. However, this tendency is not without cost—psychological costs often accompany the suppression or distortion of unfavorable information. This paper develops a formal model of optimistic belief updating that explicitly incorporates these psychological costs. We provide an axiomatic foundation for the model, called the costly Bayesian optimism (CBO) representation. Our model generalizes both Bayesian updating and the Bayesian optimism representation proposed by Saponara (2018) by introducing a cost function for belief distortion. A key contribution of this paper is to show that, under mild conditions, the psychological cost function can be uniquely identified from observed choice behavior. The model also explains stake-dependent belief distortions, a phenomenon frequently observed in laboratory experiments but not accounted for by existing axiomatic models. Furthermore, we demonstrate how modifying certain axioms yields alternative representations of belief distortion, including standard Bayesian updating and distortions toward subsets of information. Our framework thus provides a unified axiomatic framework of a broad class of belief distortions.

7月22日(火): 16:20-18:40 富士見校舎4階404教室

16:20-17:25

発表者1: 宮城島要 (一橋大学経済学研究科)

タイトル: Impartial Criteria to Evaluate Social Risk

概要: In this paper, we examine the aggregation of individual risk preferences that are ordinal and interpersonally non-comparable. We focus on social welfare criteria that satisfy a condition called Impartiality, which requires that social evaluations of individuals' final situations remain invariant under permutations of individual outcomes. By imposing additional conditions of efficiency and rationality alongside Impartiality, we characterize a class of social welfare criteria known as Certainty Equivalent Equally Distributed Equivalent (CEEDE) criteria. We investigate how CEEDE criteria reflect social attitudes toward inequality and risk, and provide characterizations of more specific criteria within the CEEDE class.

17:35-18:40

発表者2: 岡田章 (一橋大学名誉教授)

タイトル: Dynamic Bargaining and Free Trade Agreements

概要: Why does free trade not prevail in the world even when it is Pareto efficient? To consider this long-standing question in international trade, we present a dynamic bargaining game where countries form and reform free trade areas (FTAs) over periods. Countries may be politically motivated. Participants can leave FTAs if they are reversible and cannot otherwise. To overcome the undesirable property of the folk theorem in repeated games, a large multiplicity of subgame perfect equilibria with inefficient sanctions (trade war), we explicitly formulate a renegotiation process and consider a state-dependent equilibrium. We show that there exists a renegotiation-proof equilibrium where patient countries immediately agree to free trade and sustain it even when FTAs are reversible. When FTAs are irreversible, we further show that all equilibrium trade regimes converge to free trade in finitely many periods under a superadditivity condition of countries' payoffs, independent of the discount factor. We extend the free trade results to a case where transfers between countries are unavailable.

11月4日(火): 16:20-18:40 富士見校舎4階404教室

16:20-17:25

発表者1: 倉田怜於 (早稲田大学大学院経済学研究科博士期課)

タイトル: TBA

概要: TBA

17:35-18:40

発表者2: 岡田章 (慶應義塾大大学院経済学研究科博士課程)

タイトル: TBA

概要: TBA