Parties in pluralist democracies face numerous political issues that citizens may be split on, but most models of party competition assume a simple, often one-dimensional structure. A new, inherently multidimensional model of party strategy is presented, where parties compete by selectively emphasizing policy issues. Issue emphasis is determined by two distinct goals: mobilizing the party’s core voters and broadening the support base. Optimal issues for this purpose lie in between idealtypical positional and valence issues, as they need to be relatively uncontroversial within the party, while at the same time widely supported in the electorate at large. The capacity of an issue to promote both goals is captured by an integrated index labeled “issue yield.” A model based on this index is tested on a 27-country comparative dataset combining mass surveys and manifesto scores from the 2009 European Election Study. Results of multilevel tobit regressions suggest that issue yield is a powerful indicator of party strategy.

Lorenzo De Sio is Assistant Professor at LUISS Guido Carli University in Rome. His main interests are in elections, public opinion and voting behaviour, both in Italy and in comparative perspective, with a specific focus on models of voting behaviour and party competition. A member of the Scientific Committee of the Italian National Election Studies (ITANES), he is the coordinator of the Italian Center for Electoral Studies (LUISS Rome), and a member of the Methods Working Group for the “True European Voter” international research project. Besides his two books in Italian, his scientific publications include articles appearing in Comparative Political Studies, West European Politics, South European Society and Politics, Rivista Italiana di Scienza Politica. He has been Visiting Research Fellow at the University of California – Irvine, and Jean Monnet Fellow at the European University Institute.