Round-robin political tournaments: Abstention, truthful equilibria, and effective power

Abstract

A round-robin political tournament is an election format where multiple candidates contest in pairs, and votes are aggregated using a general rule to form a social ranking. We formalize this tournament as a strategic form game and provide a necessary and sufficient condition under which truthful voting is a Nash equilibrium. Building on this analysis, we study the concept of effective power, defined as a voter's ability to bring about a social ranking that maximizes his preferences. We show that the classical theories of political power do not translate into effective power in general. We then provide a full characterization of the classes of political tournaments and utility metrics for which these theories capture effective power. We offer both structural and behavioral interpretations of the findings, and derive practical implications for the design of political tournaments that are compatible with truth-telling.