Disproportionality and Party System Fragmentation: Does Assembly Size Matter?

Abstract

The article examines the impact of assembly size on the degree of disproportionality and party system fragmentation. The hypothesis is as follows: assembly size has a negative effect on the degree of disproportionality and a positive effect on the effective number of parties in systems with single-member districts—in proportional electoral systems, by contrast, such a pattern does not exist. In PR systems, notably the average effective threshold supersedes assembly size in explaining the degree of disproportionality and the effective number of parties. Electoral thresholds, ordinal ballots and apparentement, which also have some impact on disproportionality and party system fragmentation in proportional elections, are absent in systems with single-member districts (with the exception of ordinal ballots in alternative vote systems). Moreover, the district magnitude does not vary between electoral districts and countries. Therefore, assembly size is a significant factor in majoritarian systems. The empirical analysis of 550 elections in democratic countries provides support for the hypothesis.