Mixed electoral systems and electoral system effects: controlled comparison and cross-national analysis

Abstract

Utilizing data from 15 countries that employ mixed electoral systems, we provide a cross-national analysis of the defining elements and potentially constraining effects of such systems. Using district level election results, we examine the effects of the proportional representation (PR) and single-member district (SMD) tiers of mixed systems separately and in combination. We also test the effects on electoral outcomes of different components of mixed systems such as linked tiers, ratio of SMD to PR seats, and majority versus plurality rules in the SMD tier. Our findings suggest that, despite claims of a “contamination effect” between the two tiers, in countries with developed party systems, PR and SMD electoral arrangements tend to approximate their expected effects even when used in combination in mixed systems. We also find that particular institutional characteristics within mixed systems have a substantial constraining effect on the number of significant political parties. However, the nature of the party system itself, in particular the extent to which its parties are institutionalized, also plays a very important role in shaping the degree to which constraining effects are truly felt.