倉田怜於

概要

専門分野：社会的選択理論・経済哲学

日本学術振興会 特別研究員DC1 (2025–)

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出版論文

1. 2026

   A single-axiom cardinal characterisation of quadratic utility

   Economics Letters, 2026.

   掲載誌原稿

   要旨

   Chambers and Echenique (in J Econ Theory 189:105086, 2020) characterised quadratic(-plus-linear) social welfare functions using Status Quo Independence and Eventual Linearity. We show that Status Quo Independence implies the latter condition at every status quo, making it redundant. Under continuity and normalisation, Status Quo Independence solely yields a unique quadratic-plus-linear decomposition: The proof separates the even and odd parts of the social welfare function into the parallelogram equation and Jensen's equation. Eventual Linearity alone is insufficient because it leaves the even component unrestricted.

   Appendix

   Every even function $U:\mathbb{R}^n\to\mathbb{R}$ automatically satisfies EL. Indeed, if $U$ is even, then $\delta_{\mathbf{0}}(x)=U(x)-U(-x)=0$ for every $x\in\mathbb{R}^n$, so the EL-additivity holds at $w=\mathbf{0}$ for every pair $x,y\in\mathbb{R}^n$. Thus, EL imposes no restriction within the class of even functions.

ワーキングペーパー

1. 2025

   Collective decisions under uncertainty: efficiency, ex-ante fairness, and normalization

   共著：Kensei Nakamura ・ Theoretical Economics ・ R&R

   原稿DP

   要旨

   This paper studies preference aggregation under uncertainty in the multi-profile framework and characterizes a new class of aggregation rules that address classical concerns about Harsanyi’s (1955) utilitarian rules. Our aggregation rules, which we call relative fair aggregation rules, are grounded in three key ideas: utilitarianism, egalitarianism, and the 0–1 normalization of individual utilities. These rules are parameterized by a set of weight vectors over individuals and evaluate each ambiguous alternative by taking the minimum weighted sum of 0–1 normalized utility levels over the weight set. For the characterization, we propose two novel axioms—weak preference for mixing and restricted certainty independence—developed by using a new method of objectively randomizing outcomes within the Savagean setting. Additional results clarify how these axioms capture the utilitarian and egalitarian attitudes of the rules.

2. 2026

   Reservation of Judgment and Robust Collective Decisions

   共著：Kensei Nakamura ・ 査読中

   原稿

   要旨

   This paper studies preference aggregation under ambiguity when agents have incomplete preference relations due to imprecise beliefs. We introduce the “dual” of the Pareto principle, which respects unanimity among individuals, including those with unexpressed opinions. Our first theorem shows that, in most cases, this principle leads to a dictatorial rule in taste aggregation. We argue that this stems from the problem of spurious unanimity, even when the individuals have the same prior set. By weakening the above principle to avoid respecting spurious unanimity, the second theorem characterizes novel belief-aggregation rules, under which society does not discard any combination of plausible priors.

3. 2026

   Agreement with reservation of judgment under risk

   共著：Kensei Nakamura

   原稿

   要旨

   This paper studies preference aggregation under risk. In our model, each agent has an incomplete preference relation represented by a set of expected utility functions. The classical Pareto principle is silent on agreement involving indecisiveness. To examine the implications of respecting such agreement, we introduce the Paretian principle that can be applied when some individuals reserve their judgment. Our main result shows that, under this principle, for each combination of individuals’ utility functions, there exists a corresponding social utility function constructed as a weighted sum of the individual ones. These aggregation rules guarantee natural properties that the standard Pareto principle fails to ensure.

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