Horizontal and vertical spill-over in multilevel electoral systems

Abstract

A multilevel electoral system perspective reveals several ways in which electoral spill-over may occur. Vertical spill-over may be top-down from the national to the regional level or can be bottom-up from the regional to the national electoral arena. Horizontal spill-over happens when developments in one regional electoral arena impact electoral outcomes in another regional electoral arena. The literature on regional elections has mainly focused on vertical top-down spill-over. In this introduction, we discuss two main insights in relation to spill-over between electoral arenas that surface when considering the collection of articles and reports presented in this fourth annual review of regional elections. First, we discuss how horizontal spill-over can be identified and differentiated from diffusion of electoral developments driven by territorial cleavages. Second, we discuss several institutions that impact vertical spill-over. We conclude by considering a wider research agenda for the study of spill-over in multilevel electoral systems.