Introduction to the Unified Theory of Party Competition

Despite the insights provided by the standard models of party competition, these models have failed to account for some fundamental empirical regularities found throughout the democratic world. Regardless of electoral system, political parties tend to be located across a wide ideological spectrum, and parties tend to exhibit considerable consistency in their ideological locations. Many models of party competition – particularly, spatial models that emphasize electoral incentives – generate predictions that are at variance with empirical observation. Either these theories predict convergence of party positions to similar, centrist positions (Enelow and Hinich 1984; de Palma, Hong, and Thisse 1990; Hinich and Munger 1994; Lin, Enelow, and Dorussen 1999), or they predict instability in party positions and the absence of an equilibrium (Schofield 1978; McKelvey 1986). With important exceptions to be discussed later, models that follow the tradition of Anthony Downs (1957) highlight centripetal forces in party competition – forces that draw party positions toward the center of the policy spectrum. On the other hand, the main alternative approaches to spatial models – sociological models that are driven by voter demographics, and social psychological theories that rest entirely on notions of partisan loyalties – customarily fail to take into account the importance of policy issues and campaign strategies.

At the heart of this book is a desire to reconcile theory and evidence: to explain the theoretical puzzle of party divergence and to identify the factors that most strongly affect the extent of that divergence.