Measuring Electoral Bias: Australia, 1949–93

Electoral systems translate citizens' votes into seats in the legislature, and are thus critical components of democracies. But electoral systems can be unfair, insulating incumbents from adverse electoral trends, or biasing the mapping of votes to seats in favour of one party. I assess methods for measuring bias and responsiveness in electoral systems, highlighting the limitations of the popular ‘multi-year’ and ‘uniform swing’ methods. I advocate an approach that incorporates constituency-level and jurisdiction-wide variation in party's vote shares. I show how this method can be used to elaborate both the extent and consequences of malapportionment. I then present election-by-election estimates of partisan bias and responsiveness for ninety-three state and federal elections in Australia since 1949. The empirical results reported show that the coalition parties have generally ‘out-biased’ the Australian Labor party, despite some notable pro-ALP biases. The overall extent of partisan bias in Australian electoral systems, however, has generally diminished in magnitude over time.