The Evolution of Party Systems between Elections (original) (raw)

2003, American Journal of Political Science

Most existing theoretical work on party competition pays little attention to the evolution of party systems between elections as a result of defections between parties. In this article, we treat individual legislators as utility-maximizing agents tempted to defect to other parties if this would increase their expected payoffs. We model the evolution of party systems between elections in these terms and discuss this analytically, exploring unanswered questions using computational methods. Under office-seeking motivational assumptions, our results strikingly highlight the role of the largest party, especially when it is "dominant" in the technical sense, as a pole of attraction in interelectoral evolution. T he existing political science account of party competition pays little attention to the evolution of legislatures between elections, despite the fact that, in all real legislatures, there is a great deal of politics between elections. In particular, legislators may defect from one party and join another, parties may split and fuse, and the party system may thereby evolve into one quite different from that produced by the election result. This carries obvious analytical implications for modeling party competition and important normative implications for our appreciation of representative democracy. In supplying the link between the popular mandate and public policy in representative democracy, the forces that shape legislatures between elections are clearly very important. While there is a literature on party switching in the U.S. Congress (e.g., Nokken 2000), exploration of this in other contexts is very limited. Yet it is precisely in multiparty systems that the phenomenon is most prevalent and important. In the Italian legislature between 1996 and spring 2000, for instance, more than one in four deputies changed parties at least once (Heller and Mershon 2001, 2). Similar patterns of party switching can be seen in Japan (Laver and Kato, 2001), Poland (Benoit and Hayden 2001), and elsewhere (see Bowler, Farrell, and Katz 1999). At present there is very little work modeling this process in a multiparty context. Existing studies focus on party discipline (Heller and Mershon 2001), the electoral connection