On the Theory of Strategic Voting1

Abstract

Many analyses of plurality-rule elections predict the complete coor- dination of strategic voting, and hence support for only two candidates. Here I suggest that stable multi-candidate support will arise in equilibrium. A group of voters must partially coordinate behind one of two challenging candidates in order to dislodge a disliked incumbent. In a departure from existing models, the popular support for each challenger is uncertain. This support must be inferred from the private observation of informative signals, such as the social communication of pref- erences throughout the electorate, or the imperfect observation of opinion polls. The uniquely stable voting equilibrium entails only limited strategic voting and hence incomplete coordination. This is due to the surprising presence of negative feed- back: an increase in the degree of strategic voting by others reduces the incentives for an individual to vote strategically. The incentive to vote strategically is lower in relatively marginal elections, after controlling for the distance from contention of a trailing preferred challenger. A calibration of the model applied to the UK General Election of 1997 is consistent with the impact of strategic voting and the reported accuracy of voters' understanding of the electoral situation. It suggests that nearly 50 seats may have been lost by the Conservative party due to strategic voting. 1. Plurality-Rule Elections and Strategic Voting 1.1. Strategic Voting and Duverger's Law. Plurality-rule elections, where the winner is the candidate who receives the largest number of votes, are vulnerable to strategic voting: a voter might well switch away from her preferred candidate and toward a perceived leader, in the hope of exerting a greater influence over the outcome of the election. This phenomenon has long been the focus of both economic and political scientific study. In an influential essay, Riker (1982b) cited Droop's (1871) eloquent exposition of the strategic-voting problem: 1 I oer my grateful thanks to the many friends, colleagues, seminar participants, referees, and editors who have oered insightful comments during the long gestation of this paper, its antecedents, and companion work. Special thanks go to Steve Fisher, whose empirical analysis of strategic voting raised many of the questions that I seek to answer in this paper, and to Chris Wallace. This particular paper brings together much of the analysis previously circulated in the papers A New Theory of Strategic Voting, Strategic Voting Under the Qualified Majority Rule, and Idiosyncrasy, Information, and the Impact of Strategic Voting.