Mackerras Pendulum

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The Mackerras Pendulum was invented by the Australian psephologist Malcolm Mackerras as a way of predicting the outcome of an election contested between two major parties in a Westminster style lower house legislature such as the Australian House of Representatives, which is comprised of single-member electorates and which uses a preferential voting system such as a Condorcet method or IRV.

The pendulum works by lining up all of the seats held in Parliament for the government, the opposition and the cross benches according to the percentage point margin they are held by on a two party preferred basis. This is also known as the swing required for the seat to change hands. Given a uniform swing to the oppostion or government parties, the number of seats that change hands can be predicted.

[edit] External links

• Peter Brent's Federal pendulum
• Ozpolitics 2007 Australian federal pendulum