Pre-election pendulum for the next Australian federal election
The Coalition won the 2016 federal election with a one-seat majority 76 of 150 lower house seats. Labor held 69 seats while crossbenchers held the remaining five. Subsequent redistributions and a change in representation entitlement will see the number of seats in the lower house increase to 151, with one seat abolished in South Australia and one seat created in each of Victoria and the Australian Capital Territory (ACT).
This pendulum shows the notional margins for seats following boundary redistributions in Victoria, Queensland, South Australia, Tasmania, the Northern Territory and the ACT. Based on the new boundaries and their notional margins, the Coalition no longer holds a majority with 75 of 151 seats, Labor has 71 seats, with 5 crossbench seats.
Classification of seats as marginal, fairly safe or safe is applied by the independent Australian Electoral Commission using the following definition: "Where a winning party receives less than 56% of the vote, the seat is classified as 'marginal', 56–60% is classified as 'fairly safe' and more than 60% is considered 'safe'.".
The Mackerras pendulum was devised 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 composed 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 opposition or government parties, the number of seats that change hands can be predicted.
As this pendulum represents the effect of a uniform two-party swing, the results of by-elections after the 2016 federal election are ignored.