A New Spatial Theory of Party Competition: Uncertainty, Ideology and Policy Equilibria Viewed Comparatively and Temporally

This article considers how parties can decide on policy when there is no reliable information about the effect of these decisions on voting. Where this is the case they must base their stands on a priori assumptions about appropriate priorities, namely on political ideologies. These indicate the general policy area a party should occupy, but do not give detailed guidance on which position to take within it. Five different ways of deciding on this, within ideological constraints, are specified. The predictions derived from these models well anticipate the actual decisions made by post-war parties in twenty democracies, as summarized in the unique spatial maps of policy movements published by the Manifesto Research Group of the European Consortium for Political Research.