Self-attenuating Strategic Voting

This is an analysis of strategic voting under qualified majority voting. Existing formal analyses of the plurality rule predict complete coordination of strategic voting: a strict interpretation of Duverger’s Law. This conclusion is rejected. Unlike previous models, the popular support for each option is not commonly certain. Agents base their vote on both public and private signals of popular support. When private signals are the main source of information, the uniquely stable equilibrium entails only limited strategic voting and hence partial coordination. This is due to the surprising presence of negative feedback — strategic voting is a self-attenuating phenomenon. The theory leads to the conclusion that multi-candidate support in a plurality electoral system is perfectly consistent with rational voting behaviour. Incomplete. See Nuffield College DP Series for Completed Version. 1. Rethinking Strategic Voting Duverger (1954) introduced his Law to political economy by noting that “the simple-majority single-ballot system favors the two-party system”. His aim was to evaluate the effect of voting systems on the structure and number of political parties. Duverger’s writing envisaged an ongoing process involving both voters and political parties with bipartism as an eventual conclusion. More recent authors have offered a stricter version of Duverger’s Law. The models of Cox (1994), Palfrey (1989) and Myerson and Weber (1993) predict strict bipartism as the outcome of any plurality rule election. Palfrey’s (1989) “mathematical proof” claims that: “. . . with instrumentally rational voters and fulfilled expectations, multicandidate contests under the plurality rule should result in only two candidates getting any votes.” These authors consider a population of agents each casting a single vote, where the candidate with the largest number of votes wins. They claim that the uniquely stable equilibrium outcome This paper is based on part III of Myatt (1999). Stephen D. Fisher inspired this work with his extensive empirical research on tactical voting, and with many hours of conversation on the topic. Grateful thanks are also due to David Firth, Geoff Evans, Iain McLean, Chris Wallace and seminar participants at Oxford, UCL, LSE and Edinburgh for helpful comments. Robin Mason is entirely responsible for any remaining errors, due to his nagging request to get the paper finished prior to a Southampton seminar. Cheers Robin. 1 SELF-ATTENUATING STRATEGIC VOTING 2 ...................................................................................................................................................................................................................................................................................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... ..... ..... ..... ..... ..... ..... ..... ...... ....... ....... ....... ....... ....... ....... ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .