Academic journal article AEI Paper & Studies

Strategic Voting in Proportional Representation Systems

Academic journal article AEI Paper & Studies

Strategic Voting in Proportional Representation Systems

Article excerpt

Strategic voting (1) has been an important topic in psephology as researchers try to understand the ways in which voters decide how to cast their votes. Do they simply vote for their "preferred" party? Or do they target electoral outcomes and derive their vote in a more "strategic" manner? There is no shortage of research documenting that strategic voting figures prominently across electoral systems. Examining 32 elections in 32 countries, Hobolt and Karp (2010) find that, on average, sincere voting can at best account for 85 percent of votes cast, leaving ample room for strategic considerations to play an important role. (2)

Ultimately, however, what we as researchers want to understand about strategic voting is: How does it work? How does a strategic voter decide whom to cast his vote for? That is, we want to get inside the black box and understand the decision-making process. This is a much easier undertaking in a plurality system than it is in a proportional representation system (henceforth PR system). As early as 1869, Henry Droop, an English proponent of proportional representation and the inventor of the Droop quota (3), described the decision-making process in pointing out the susceptibility of plurality systems to strategic voting:

Each elector has practically only a choice between two candidates or sets of candidates. As success depends upon obtaining a majority of the aggregate votes of all the electors, an election is usually reduced to a contest between the two most popular candidates or sets of candidates. Even if other candidates go to the poll, the electors usually find out that their votes will be thrown away, unless given in favour of one or other of the parties between whom the election really lies (quoted in Riker 1982: 756).

Here, we have the strategic voter's decision-making process in a plurality system in a nutshell: he votes for that one of the two leading candidates whose policy position he likes better.

As a result of the relatively simple nature of this strategic voting process, strategic voting in plurality systems is a well understood topic. The most famous formulation of the importance of strategic voting in plurality systems is Duverger's (1954: 217) law that "the simple-majority single-ballot system favors the two-party system." Palfrey (1989) formalizes Duverger's notion and shows that in equilibrium voters coordinate on only two candidates, withdrawing support from a possible third candidate.

Understanding strategic voting in PR settings, on the other hand, has proved to be a much more elusive goal. Duverger even thought that voters in PR systems have no incentive at all to vote strategically as their vote would count in terms of representation, that is, they would not throw their vote away by not voting for one of the top two parties (cf. Hobolt and Karp 2010: 300-301). A few studies have made some headway in formally examining strategic voting in PR systems (Austin-Smith and Banks 1988, Cox and Shugart 1996, Cox 1997, Baron and Diermeier 2001, and Kedar 2005), but we still lack a convincing model of the strategic voter's decision-making process.

With this paper, we hope to contribute to opening the lid of the black box that is strategic voting in PR systems: we propose a decision-theoretic model of strategic voting. In this model, strategic voters know that they can change at most one seat from one party to another. They then decide which party to vote for based on an assessment of their votes' impact on the likelihood of different coalitions and the associated expectations of implemented policy. That is, we let our voters behave as the definition of strategic voting (see Footnote 1) implies they should behave, i.e. by "casting a ballot that maximizes their expected payoff from voting."

This paper is structured as follows: we first discuss the existing empirical evidence for voters in PR systems taking into account coalition considerations. …

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