Issue Yield and Party System Change: How Parties Integrate New Issues

The issue yield model (De Sio/Weber in APSR 2014) has introduced and validated a theory of the heresthetic use of policy issues as strategic resources in multidimensional party competition. In this paper we apply the model to the long-term dynamics of party system change. We argue that parties integrate new conflicts and issues into their platforms in a selective fashion, through a strategic assessment of the electoral potential of each new issue as captured by the issue yield model. We test our argument – and provide an example research design – using public opinion and party platform data from the 1970s to the 2010s in Western Europe, with specific reference to the emergence of post-materialist issues, while discussing data availability considerations for the immigration issue. We first describe how the emergence of new issues and conflicts presents different issue yields (i.e. different configurations of electoral risks and opportunities) for different parties. We then trace how such issues become selectively integrated into party platforms and how these dynamics can be predicted using the issue yield index. Overall, our analysis provides a theoretical and empirical account of the restructuring of the political space.