Electoral System, Voter Preferences, and the Fragmentation of Party System: The East Asian Cases

Abstract

It has been demonstrated that, as an indicator of the fragmentation of political system, the effective number of candidates running under the single nontransferable vote (SNTV) system converges to M+1, where M is district magnitude. How these candidates are to be grouped into parties, however, remains unanswered. I propose that the effective number of parties under SNTV is determined by electoral system as well as the voters' preference profiles. When the voters are idealistic and select the candidates according to their issue positions, the centrifugal tendency of SNTV fosters M+1 effective parties. When the voters care only about absolute gains, the need to maintain a stable distributive coalition encourages one-party dominance, unless regionalism hinders the formation of a grand national party. Using the percentage of agricultural population to approximate the proportion of realist voters, I show that this formula explains well the evolution of party systems in Japan, South Korea, and Taiwan.