Research question/goal:

To explain an empirical puzzle that the party system in West German plurality tier is closer to bipartism with high-level linkage than under the British plurality system, this project proposes an interactive mechanism between both tiers of mixed-member electoral systems. The distinctive feature of the model lies in interactive effects in terms of expectation formation. That is, voters under mixed systems are assumed to utilize national-level PR results to form expectations which, in turn, are used to vote strategically in plurality tier. To obtain empirically testable macro-level implications, this project developed a computational model and examines its simulation results. The simulation results show that the party system in districts dominated by the two main parties’ candidates is strongly characterized by Duvergerian equilibrium if voters utilize national-level PR results to form expectations. This macro-level implication was systematically integrated in analyzing aggregate-level data via Bayesian statistics. The results show that voters’ expectation formation in West Germany, New Zealand and Japan are oriented by the national-level PR results increasingly after introducing mixed systems. The exceptional development in East Germany was attributed to deviating party systems in the state-level parliaments.