Conceptualizing and measuring territorial heterogeneity in the vote

Territorial inequalities between regions are very often linked territorial heterogeneity in the vote. Statewide parties receive different degrees of support across the statewide territory (Bochsler 2010; Caramani 2004; Scott-Morgernstern 2017) which has a huge impact on the extent to which policy diverges between regions (Toubeau and Kleider 2022). Similarly, regional identities are mobilized to different degrees by regional parties that compete in some but not other regions which hugely impacts the extent to which citizens support intergovernmental transfers and fiscal equalization between regions (Henderson et al. 2014; Schakel and Brown 2021). Hence, understanding the causes and consequences of territorial inequalities between regions requires a proper conceptualization and measurement of territorial heterogeneity in the vote. Most progress has been made regarding the exploration into when, where, and how parties are able to attract voters across the statewide territory (Bochsler 2010; Caramani 2004; Scott-Morgernstern 2017). Recently, this research has been criticized for not exploring when, where and how the vote is different for (certain) regions (Schakel 2013). This paper has two main research objectives. First, it provides a critical review of the literatures on nationalization of and congruence between regional and national party systems and lays bare the most important assumptions that underlie the various conceptualizations and measurements on the territorial heterogeneity of the vote. Second, we argue that a full understanding of the dynamics and outcomes in any electoral arena in Europe requires the conceptualization of a multilevel electoral system that includes electoral arenas from the local to the European level. Most indicators of party (system) nationalization and congruence between party systems compare regional to statewide election results. This kind of indicators have clearly revealed that methodological nationalism has heavily impacted the research of nationalization scholars but, at the same time, an over-reliance on these indicators may give rise to ‘methodological regionalism’. That is, the use of indicators that take the region as unit of analysis to explain regional divergence without taking the multilevel electoral context into account. To avoid a potential ‘methodological regionalism bias’ we suggest that one needs to conceptualize and measure electoral spill-over between electoral arenas at three or more territorial scales. We proceed by conceptualizing and developing indicators for regional distinctiveness regarding the vote in European in addition to the national, and regional elections for 289 regions in 15 Western European countries for 3,210 elections held since 1950. Through explorative analyses we assess the importance of various causes of territorial heterogeneity in the vote –i.e. regional identity, regional authority, and regional electoral institutions—and we explore the impact of territorial heterogeneity in the vote on citizens’ preferences for interregional fiscal transfers between the member states of the EU as well as between regions within the members states.