Moderation in Proportional Systems: Coalitions Matter

Abstract

This paper examines the role of the coalition formation process in a proportional system. It models its impact on the voters (who maximize their expected utilities) and the parties (who choose their platforms in a Nash game). In contrast with the intuitive idea that proportional systems represent “proportionally”, I show that a proportional system with minimal range coalitions leads to party convergence towards the median of the political spectrum. Indeed, a political party’s prospects of power are better when it is more likely to find ideological partners, i.e. when it is not ideologically isolated. In contrast, if coalitions are formed according to a minimum winning coalition rule a la Riker, any policy can be implemented in equilibrium.