arXiv subjects

Kensei Nakamura

Publications and source records attributed to Kensei Nakamura.

14 recordsLinked to original sources

arXiv2026

Cautious and fair social evaluation under risk

In this paper, we study criteria for social evaluation of resource distributions under risk when individuals have expected utility preferences but their utility functions are interpersonally non-comparable. In particular, we focus on cautious evaluation with respect to ex-post distributions. As a key rationality axiom, we adopt Negative Certainty Independence, introduced by Dillenberger (2010). Using this axiom together with Pareto conditions that are compatible with both the rationality axiom and ex-post equity, we characterize a class of social criteria called Cautious Equally Distributed Equivalent (CEDE) criteria. These criteria evaluate risky situations by the lowest certainty equivalent over a set of social utility functions constructed from individual utility functions.

econ.TH↗

arXiv2026

Randomization and ambiguity perception

Ambiguity-averse decision makers typically dislike not only the presence of ambiguous events but also their increase, contrary to what standard ambiguity models predict. We axiomatically study such a decision maker. She avoids ex ante randomization over prospects since it only increases the number of relevant ambiguous events without providing a hedge against uncertainty. Our axioms lead to a representation in which the decision maker behaves as if optimizing her ambiguity perception at a cost. We show the uniqueness of the representation, and conduct comparatives of attitudes toward ambiguity and its increase. This identification is not achieved without considering ex ante randomization.

econ.TH↗

arXiv2026

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

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.

econ.TH↗

arXiv2026

Condorcet-loser dominance among scoring rules

This paper studies a dominance relation among scoring rules with respect to avoiding the selection of the Condorcet loser. In a voting model with three or more alternatives, we say that a scoring rule $f$ Condorcet-loser-dominates (CL-dominates) another scoring rule $g$ if the set of profiles where $f$ selects a Condorcet loser is a proper subset of the set where $g$ does. We show that the Borda rule not only CL-dominates all other scoring rules, but also is the only scoring rule that CL-dominates some scoring rule.

econ.TH↗

arXiv2026

When is it (im)possible to respect all individuals' preferences under uncertainty?

When aggregating Subjective Expected Utility preferences, the Pareto principle leads to an impossibility result unless the individuals have a common belief. This paper examines the source of this impossibility in more detail by considering the aggregation of a general class of incomplete preferences that can represent gradual ambiguity perceptions. Our result shows that the planner cannot avoid ignoring some individuals unless there is a probability distribution that all individuals agree is most plausible. This means that even if individuals have similar ambiguity perceptions, the impossibility persists as long as some individual's most plausible belief differs even slightly from that of others.

econ.TH↗

arXiv2026

Agreement with reservation of judgment under risk

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.

econ.TH↗

arXiv2025

The Coarse Nash Bargaining Solutions

This paper studies the axiomatic bargaining problem and proposes a new class of bargaining solutions, called coarse Nash solutions. These solutions assign to each problem a set of outcomes coarser than that chosen by the classical Nash solution (Nash, 1950). Our main result shows that these solutions can be characterized by new rationality axioms for choice correspondences, which are modifications of Nash's independence of irrelevant alternatives (or more precisely, Arrow's (1959) choice axiom), when combined with standard axioms.

econ.TH↗

arXiv2025

Reservation of Judgment and Robust Collective Decisions

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.

econ.TH↗

arXiv2025

Partially rational preferences under ambiguity

Completeness and transitivity are standard rationality conditions in economics. However, under ambiguity, decision makers sometimes violate these requirements because of the difficulty of forming accurate predictions about ambiguous events. Motivated by this, we study various ambiguity preferences that partially satisfy completeness and transitivity. Our characterization results show that completeness and a novel yet natural weakening of transitivity correspond to two opposite ways of using multiple probability distributions in mind; that is, these two axioms have dual implications at the level of cognitive processes for ambiguity.

econ.TH↗

arXiv2025

Cautious Dual-Self Expected Utility and Weak Uncertainty Aversion

Gilboa and Schmeidler's (1989) uncertainty aversion plays a central role in decision theory and economics, yet many inconsistent behaviors have been observed in experiments. Motivated by this, we study an axiom postulating a minimal degree of uncertainty aversion. Our main result shows that this axiom yields a new class of representations, called cautious dual-self expected utility representations. In this model, two selves in the decision maker's mind play an extensive-form game to determine the belief used for evaluation, where the first mover is selected cautiously. As illustrated by two alternative representations, cautiously choosing between two "dual" scenarios is the key implication of our axiom.

econ.TH↗

arXiv2025

Preferences with Multiple Forecasts

When a collective decision maker presents a menu of uncertain prospects to her group members, each member's choice depends on their predictions about payoff-relevant states. In reality, however, these members hold different predictions; more precisely, they have different prior beliefs about states and predictions about the information they will receive. In this paper, we develop an axiomatic framework to examine collective decision making under such disagreements. First, we characterize two classes of representations: Bewley multiple learning (BML) representations, which are unanimity rules among predictions, and justifiable multiple learning (JML) representations, where a single prediction has veto power. Furthermore, we characterize a general class of representations called hierarchical multiple learning representations, which includes BML and JML representations as special cases. Finally, motivated by the fact that these representations violate completeness or intransitivity due to multiple predictions, we propose a rationalization procedure for constructing complete and transitive preferences from them.

econ.TH↗

arXiv2025

Social Choice Rules with Responsibility for Individual Skills

This paper examines normatively acceptable criteria for evaluating social states when individuals are responsible for their skills or productivity and these factors should be accounted for. We consider social choice rules over sets of feasible utility vectors à la Nash's (1950) bargaining problem. First, we identify necessary and sufficient conditions for choice rules to be rationalized by welfare orderings or functions over ability-normalized utility vectors. These general results provide a foundation for exploring novel choice rules with the normalization and providing their axiomatic foundations. By adding natural axioms, we propose and axiomatize a new class of choice rules, which can be viewed as combinations of three key principles: distribution according to individuals' abilities, utilitarianism, and egalitarianism. Furthermore, we show that at the axiomatic level, this class of choice rules is closely related to the classical bargaining solution introduced by Kalai and Smorodinsky (1975).

econ.TH↗

arXiv2025

Weak independence of irrelevant alternatives and generalized Nash bargaining solutions

In Nash's (1950) seminal result, independence of irrelevant alternatives (IIA) plays a central role, but it has long been a subject of criticism in axiomatic bargaining theory. This paper examines the implication of a weak version of IIA in multi-valued bargaining solutions defined on non-convex bargaining problems. We show that if a solution satisfies weak IIA together with standard axioms, it can be represented, like the Nash solution, using weighted products of normalized utility levels. In this representation, the weight assigned to players for evaluating each agreement is determined endogenously through a two-stage optimization process. These solutions bridge the two dominant solution concepts, the Nash solution and the Kalai-Smorodinsky solution (Kalai and Smorodinsky, 1975). Furthermore, we consider special cases of these solutions in the context of bargaining over linear production technologies.

econ.TH↗

arXiv2025

Impartial utilitarianism on infinite utility streams

When evaluating policies that affect future generations, the most commonly used criterion is the discounted utilitarian rule. However, in terms of intergenerational fairness, it is difficult to justify prioritizing the current generation over future generations. This paper axiomatically examines impartial utilitarian rules over infinite-dimensional utility streams. We provide simple characterizations of the social welfare ordering evaluating utility streams by their long-run average in the domain where the average can be defined. Furthermore, we derive the necessary and sufficient conditions of the same axioms in a more general domain, the set of bounded streams. Some of these results are closely related to the Banach limits, a well-known generalization of the classical limit concept for streams. Thus, this paper can be seen as proposing an appealing subclass of the Banach limits by the axiomatic analysis.

econ.TH↗