The advantages of ideological cohesion: a model of constituency representation and electoral competition in multi-party democracies

This article develops a model of parties in multi-party systems. Instead of treating parties as vote-maximizing candidates able to take any position, parties are assumed to be controlled or at least constrained by their supporters. The model relies on a process whereby supporters sort themselves between parties, as in Aldrich (1983) and the economics literature starting with Tiebout (1956). The results of the model are sensitive to the shape of the preference distribution, particularly its skewness. This can be used to explain how a cohesive minority may have more influence than a more dispersed majority, and why certain parties are systematically advantaged over others.