Multidimensional Party Polarization in Europe: Cross-Cutting Divides and Effective Dimensionality

Abstract

Ideological polarization matters. It is a necessary requirement for meaningful electoral competition, but at its extreme can strain democratic functioning. The conceptualization and measurement of contemporary ideological polarization is complicated by the growing complexity of the policy differences between political parties. Yet, existing indicators remain one-dimensional in nature, despite the wide acceptance of the multidimensional structure of European politics. To resolve this tension, we introduce a novel, two-dimensional measure of party polarization. Using the correlation matrix of parties’ ideological positions, we calculate the effective dimensionality of a political space, which accounts for the degree to which the dimensions crosscut each other. We highlight the advantages of this approach with both artificial data and positional estimates derived from the Chapel Hill Expert Survey (1999-2019). Then, we explore the empirical implications of our multidimensional measurement strategy, and show that it is better suited to capture the relationship between party polarization and mass partisanship. This study has important theoreti- cal, methodological, and normative implications for our understanding of democratic representation in a changing political landscape.