Liberal political equality implies proportional representation

This article shows that for a single-vote electoral system for a representative body to treat all voters and all parties equally, it must produce results essentially identical to list proportional representation (PR). Democratic theory has often been agnostic concerning representative institutions. Different institutions have been compared in terms of behavioral outcomes rather than axiomatic properties. Building on van der Hout (Annual meeting of the Public Choice Society, San Diego, 2002) result, we show that for an electoral system to completely respect the principle of liberal political equality and popular sovereignty, its results must be equivalent to those of list PR.