Issue yield: a model of party strategy in multidimensional space

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. We develop a new, inherently multidimensional model of party strategy in which parties compete by emphasizing policy issues. Issue emphasis is determined by two distinct goals: mobilizing the party’s core voters and broadening the support base. Accommodating these goals dissolves the position-valence dichotomy because it requires emphasizing policies that are 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.” We test a yield-based model on a 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. Word count (including references, tables, figures, and appendices): 11,996