Issue Yield: A Model of Party Strategy in Multidimensional Space

Parties in pluralist democracies face numerous contentious issues, but most models of electoral 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 informed by two distinct goals: mobilizing the party's core voters and broadening the support base. Accommodating these goals dissolves the position-valence dichotomy through a focus on policies that unite the party internally while also attracting support from the electorate at large. We define issue yield as the capacity of an issue to reconcile these criteria, and then operationalize it as a simple index. Results of multilevel regressions combining population survey data and party manifesto scores from the 2009 European Election Study demonstrate that issue yield governs party strategy across different political contexts.