The Mean Voter Theorem: Necessary and Sufficient Conditions for Convergent Equilibrium

Formal models of elections have emphasized the convergence of party leaders towards the centre of the electoral distribution. This paper attempts to resolve the apparent disparity between the formal result and the perception of political divergence by considering a model incorporating valence. Valence can be interpreted as the non-policy basis of political judgement made by the electorate concerning the quality of political contenders. The theorem presented here shows that there is a necessary condition for convergence. The condition involves the difference in party valences and the electoral variance. When the condition fails, the low-valence parties will be forced to adopt policy positions far from the electoral centre. The inference appears to be substantiated by an empirical model of the Israel election in 1996.