Are Voters Equal under Proportional Representation?

We develop and apply a new conceptual framework and measure for evaluating electoral systems, focusing on (in)equality in parliamentary representation. Our main arena of interest is proportional representation with districts, an electoral system employed by more than half of democratic states, and we draw on an almost entirely overlooked fact: Electoral regimes vary substantially within countries, with some voters casting their ballot in semi-majoritarian districts of few representatives and others in large and proportional ones. This within-country institutional variation, we contend, affects representational (in)equality. Evaluating equality in parliamentary representation, we demonstrate that districted proportional representation often leads to overrepresentation of voters supporting right-leaning parties. Utilizing district-level data from 20 Western parliamentary democracies and complementing our within-country approach with a cross-country analysis, we further show that where parliaments are elected by large and small districts, representational inequality among voters is greater compared with countries in which parliament is elected by even-magnitude districts.