RIEB Discussion Paper Series No.2025-12

Title

Assistance-proofness

Abstract

We consider situations in which the final ranking of candidates is determined by rankings of multiple factors. For example, in Formula 1 racing, the annual ranking is determined by the results of many races. In sport climbing, the final ranking is determined by combining the results of two or three events. Dependent on rules that aggregate rankings across multiple factors, a candidate can improve the final position of a fellow candidate by holding back her performance without dropping the final position. We call the property of rules that prevent this kind of strategic manipulation assistance-proofness. We show that when there are four or more events, no scoring rule other than the null rule satisfies assistance-proofness. However, when there are two events, all dichotomous scoring rules satisfy assistance-proofness. For three events, we characterize a subclass of dichotomous scoring rules that satisfy assistanceproofness.

Keywords

Assistance-proofness; Scoring rules; Voting; Strategic manipulation; Collusion

JEL Classification

D71, D72

Inquiries

Ryoga DOI*
Graduate School of Economics, Keio University
Junior Research Fellow, RIEB, Kobe University

*This Discussion Paper won the Kanematsu Prize (FY 2024).