Introduction

Our central goal has been to integrate the spatial model of elections, which posits that policy considerations are the dominant influence on voter choice, with the behavioral model, in which voters are moved by a mixture of nonpolicy as well as policy issues. We believe that by merging the behavioral perspective and the spatial modeling paradigm associated with rational choice theory, we can provide insights into parties' election strategies that neither approach provides by itself. We label our behavioral–rational choice hybrid the unified theory of party competition.

We have used our unified theory to explain – both theoretically and empirically – parties' and presidential candidates' election strategies in several Western democracies. Theoretically, we have presented a systematic account of how the strategic incentives of vote-seeking parties vary with a multitude of factors, including the size and extremity of partisan constituencies, the number of parties, the dispersion of voters' policy preferences, the electoral salience of policies, the degree to which voters discount the parties' policy promises, and the extent to which voter abstention is motivated by alienation. We have also presented an algorithm – one that can be applied to election survey data – that can quickly locate equilibrium policy configurations for vote- or margin-maximizing parties, and that can be used to evaluate whether any computed equilibrium configuration is unique.

Empirically, we have applied the unified model of party competition in an effort to account for the observed policy positions of parties and presidential candidates in four diverse democracies: France, Norway, Britain, and the United States. Specifically, we have estimated the parameters for alternative voting models using election survey data from these four countries.