Gallagher index

The Gallagher index measures an electoral system's relative disproportionality between votes received and seats in a legislature.

[3] The Gallagher index is a statistical analysis methodology utilised within political science, notably the branch of psephology.

The index is therefore commonly abbreviated as "LSq" even though the measured allocation is not necessarily a least squares fit.

The first publication of the use of least squares in measuring the dis-proportionality of election outcomes was by Michael Gallagher in 1991[7] in which he writes: "These [election] indices were originally outlined in Markku Laakso and Rein Taagepera, ‘ “Effective” number of parties: a measure with application to west Europe’, Comparative Political Studies 12:1 (1979), pp.

The committee recommended that "the government should seek to design a system that achieves a Gallagher score of 5 or less.

This table uses for example the 2012 Queensland state election, one of the largest landslides in Australian electoral history.

Though Australia and New Zealand have somewhat similar political histories, Australia uses preferential voting in Single-member districts for Commonwealth House of Representative and most state and territory Legislative Assembly elections, which tends to result in far less proportionality compared to New Zealand's MMP system (or other proportional electoral systems), especially for larger minor parties, such as The Greens or, historically, the Australian Democrats.

The 2012 Queensland election had an extremely high Gallagher Index, at 31.16, due to the massive landslide in seats for the victorious LNP.

The Republic of Ireland uses the single transferable vote (STV) system with Droop quota in elections to the Dáil Éireann.