Assessing the mechanical and psychological effects of district magnitude

Abstract

District magnitude is a central aspect of the institutional context in PR elections, and it influences parties’ and voters’ strategies. The incentives for strategic behaviour are stronger in smaller districts, as only large parties are likely to be viable. This article investigates how much the vote is affected by this characteristic of the electoral context, focusing on the 2005 and 2009 Portuguese elections. Portugal is one of the countries with the largest degree of variation in district magnitude and represents thus an ideal case for analysing district magnitude effects. Relying on data from the Comparative Study of Electoral Systems, this study shows a strong mechanical effect of district magnitude and a limited psychological effect.