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Toshiya Yoshimura

Publications and source records attributed to Toshiya Yoshimura.

2 recordsLinked to original sources
arXiv2026

Coalitional Manipulation and Target Set Correspondences

We study coalitional manipulation of interval-valued social choice correspondences on the single-peaked domain. In the single-valued model, strategy-proofness and group strategy-proofness coincide within the standard class of peaks-only social choice functions, so generalized median voter rules retain their robustness to coalitional manipulation. This equivalence breaks down once the outcome is allowed to be set-valued: generalized median correspondences may be strategy-proof while remaining vulnerable to coordinated deviations. We show that, among generalized median correspondences allowing genuine set-valued choice, pairwise strategy-proofness already forces anonymity. With voter sovereignty, this restriction becomes sharp and characterizes target set correspondences. Thus, the target-set structure emerges as the form of set-valued flexibility compatible with pairwise coalitional robustness.

econ.TH↗
arXiv2026

Peak-Robust Voting Rules

This paper proposes new robustness criteria for social choice correspondences under single-peaked preferences, inspired by the concepts of robustness in statistical estimation, where robust estimators are designed to be resilient to both model misspecification and outliers. Motivated by robustness to model assumptions, we introduce peak-robustness: a voting rule is peak-robust if it never selects an alternative that is a majority loser relative to some unchosen alternative for any preference profile sharing the same peak profile. To capture robustness to outliers, we propose tail-invariance, which requires that variations in the tails of the peak distribution do not affect the collective decision. Our main result shows that the median voting rule is the unique efficient rule satisfying these robustness criteria. When peak-robustness is weakened, we characterize the broader class of quantile rules. Taken together, these results provide a robustness-based axiomatic foundation for median and quantile voting rules, independent of the traditional strategy-proofness approach.

econ.TH↗