A Universal Measure of the Proportionality of Electoral Systems

Daniel Bochsler (University of Copenhagen)

5th june 2018, 15:00h, Sala de Juntes de la Facultat de Ciència Política i Sociologia de la UAB
For the literature in comparative politics, comparative political economy, and in conflict studies the proportionality of the electoral system is one of a few key variables characterising the domestic political institutions. While district magnitude is the most important determinant of the proportionality of an electoral system, there is no commonly accepted operationalisation of it in the growing family of electoral systems with legal thresholds, or in mixed electoral systems. This article proposes a new measure of the proportionality of electoral systems, the universal district magnitude. Empirically, the article compares how different measures of district magnitude perform, when explaining the two most direct consequences of electoral systems: the number of parties, and vote-seat-disproportionality, relying on the results of 400 elections in 69 democracies.