When electoral competition determines disproportionality: Majority bonus and regional elections in France and Italy

This article investigates the effect of the changing format of electoral competition on the level of disproportionality in a peculiar type of mixed electoral system: the majority bonus system. It examines the last three regional elections in France and Italy. Both countries share defining characteristics: they use the majority bonus system in regional elections, and they have both been characterized by the emergence or the surge of a strong third pole refusing any alliance with other parties in a party system that was previously characterized by fragmented bipolarism. Using several scenarios of vote repartition, descriptive statistics, and an OLS regression, we show that the electoral size of the third pole and the closeness of the race between the two main contenders in given regional contests both contribute to a significant rise in the level of disproportionality. More broadly, this rising level of disproportionality implies consequences that are not to be discarded for the quality of representation in France and Italy.