Welfare effects of strategic voting under scoring rules

TL;DR

This paper investigates how strategic voting under scoring rules impacts social welfare, revealing that manipulation generally reduces welfare and often leads to different optimal rules compared to sincere voting.

Contribution

It provides a numeric analysis of the welfare effects of manipulation under scoring rules, highlighting the typical negative impact and the change in optimal rules.

Findings

Manipulation usually decreases social welfare.

Optimal voting rules differ with manipulation versus sincere voting.

Most cases show negative welfare effects from strategic voting.

Abstract

Strategic voting, or manipulation, is the process by which a voter misrepresents his preferences in an attempt to elect an outcome that he considers preferable to the outcome under sincere voting. It is generally agreed that manipulation is a negative feature of elections, and much effort has been spent on gauging the vulnerability of voting rules to manipulation. However, the question of why manipulation is actually bad is less commonly asked. One way to measure the effect of manipulation on an outcome is by comparing a numeric measure of social welfare under sincere behaviour to that in the presence of a manipulator. In this paper we conduct numeric experiments to assess the effects of manipulation on social welfare under scoring rules. We find that manipulation is usually negative, and in most cases the optimum rule with a manipulator is different to the one with sincere voters.