The Electoral System, the Party System and Accountability in Parliamentary Government

Electoral accountability requires that voters have the ability to constrain the incumbent government's policy-making power. We express the necessary conditions for this claim as an accountability identity in which the electoral system and the party system interact to shape the accountability of parliamentary governments. Data from 400 parliamentary elections between 1948 and 2012 show that electoral accountability is contingent on the party system's bipolarity, for example, with parties arrayed in two distinct blocs. Proportional electoral systems achieve accountability as well as majoritarian ones when bipolarity is strong but not when it is weak. This is because bipolarity decreases the number of connected coalitions that incumbent parties can join to preserve their policy-making power. Our results underscore the limitations that party systems place on electoral reform and the benefits that bipolarity offers for clarifying voters' choices and intensifying electoral competition.