Mackerras pendulum

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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.

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The pendulum works by lining up all of the seats held in Parliament for the government, the opposition and the crossbenches 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.

Two-party-preferred percentage

The candidate with the fewest votes is eliminated and redistributed to the voter's next choice until two candidates are left to gain a two-party-preferred figure. 2PP counting flowchart.svg
The candidate with the fewest votes is eliminated and redistributed to the voter's next choice until two candidates are left to gain a two-party-preferred figure.
Two-party-preferred polling by Newspoll, ACNielsen, Roy Morgan and Galaxy between the 2004 and 2007 federal election. Pollchart-tpp-event.svg
Two-party-preferred polling by Newspoll, ACNielsen, Roy Morgan and Galaxy between the 2004 and 2007 federal election.

The two-party preferred (2PP) method of prediction attempts to estimate the flow of second and subsequent preferences from smaller parties in order of their expected elimination during the instant-runoff voting process, to establish ultimately which major party the voters will choose – Labor or Coalition (Liberal/National) in the Australian context. A Coalition 2PP of 51% would mean a Labor 2PP of 49% and vice versa. Whichever party polls the higher two-party-preferred percentage at the election usually holds the majority of seats to form government. Exceptions to this since 2PP was introduced in 1949 were in 1954 (49.3%), 1961 (49.5%), 1969 (49.8%), 1990 (49.90%), and 1998 (49.02%). 1940 was estimated to have been won on 49.7%.

Mackerras has taken account of fully distributed transferable preference votes since the 1983 federal election. Previously, he estimated a two-party-preferred outcome from limited, selective consideration of preferences.

The largest two-party-preferred election result for the Liberal Party of Australia was at the 1966 federal election, on 56.9%, while the largest two-party-preferred election result for the Australian Labor Party was at the 1983 federal election, on 53.23 percent. The largest unofficial result was 58.2% for Labor at the 1943 federal election, estimated by Mackerras. [1]

Considering two-party-preferred estimates going back to the 1949 election, the swing to Labor at the 2007 federal election was the third-largest two-party swing, behind Malcolm Fraser and the coalition in 1975 on 7.4 percentage points and Gough Whitlam and Labor in 1969 on 7.1 points.

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The term swing refers to the extent of change in voter support, typically from one election or opinion poll to another, expressed as a positive or negative percentage point. For the Australian House of Representatives and the lower houses of the parliaments of all the states and territories except Tasmania and the ACT, Australia employs preferential voting in single-member constituencies. Under the full-preference instant-runoff voting system, in each seat the candidate with the lowest vote is eliminated and their preferences are distributed, which is repeated until only two candidates remain. While every seat has a two-candidate preferred (TCP) result, seats where the major parties have come first and second are commonly referred to as having a two-party-preferred (TPP) result. The concept of "swing" in Australian elections is not simply a function of the difference between the votes of the two leading candidates, as it is in Britain. To know the majority of any seat, and therefore the swing necessary for it to change hands, it is necessary to know the preferences of all the voters, regardless of their first preference votes. It is not uncommon in Australia for candidates who have comfortable leads on the first count to fail to win the seat, because "preference flows" go against them.

Two-party-preferred vote Result of an election or opinion poll after preferences have been distributed to the highest two candidates

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The following pendulum is known as the Mackerras pendulum, invented by psephologist Malcolm Mackerras. Designed for the outcome of the 2007 federal election, the pendulum works by lining up all of the seats held in Parliament, 83 Labor, 55 Liberal, 10 National, and 2 independent, according to the percentage point margin on a two candidate preferred basis, as elected in 2007. The two candidate result is also known as the swing required for the seat to change hands. Given a uniform swing to the opposition or government parties in an election, the number of seats that change hands can be predicted. Swing is never uniform, but in practice variations of swing among the Australian states usually tend to cancel each other out. Seats are arranged in safeness categories according to the Australian Electoral Commission's classification of safeness. "Safe" seats require a swing of over 10 per cent to change, "fairly safe" seats require a swing of between 6 and 10 per cent, while "marginal" seats require a swing of less than 6 per cent.

The following pendulum is known as the Mackerras pendulum, invented by psephologist Malcolm Mackerras. Designed for the outcome of the 2010 federal election, the pendulum works by lining up all of the seats held in Parliament, 72 Labor, 72 Coalition, 1 Nationals WA, 1 Green and 4 independent, according to the percentage point margin on a two candidate preferred basis. The two party result is also known as the swing required for the seat to change hands. Given a uniform swing to the opposition or government parties in an election, the number of seats that change hands can be predicted. Swing is never uniform, but in practice variations of swing among the Australian states usually tend to cancel each other out. Seats are arranged in safeness categories according to the Australian Electoral Commission's classification of safeness. "Safe" seats require a swing of over 10 per cent to change, "fairly safe" seats require a swing of between 6 and 10 per cent, while "marginal" seats require a swing of less than 6 per cent.

2012 Northern Territory general election

The Northern Territory general election was held on Saturday 25 August 2012, which elected all 25 members of the Legislative Assembly in the unicameral Northern Territory Parliament. The 11-year Labor Party government led by Chief Minister Paul Henderson was defeated in their attempt to win a fourth term against the opposition Country Liberal Party led by opposition leader Terry Mills with a swing of four seats, losing the normally safe Labor remote seats of Arafura, Arnhem, Daly and Stuart, whilst retaining their urban seats picked up at the 2001 election.

The following is a pendulum based on the outcome of the 2010 federal election and changes since, including the redistributions of seats in South Australia and Victoria. It is a Mackerras pendulum, invented by psephologist Malcolm Mackerras, which works by lining up all of the seats held in Parliament according to the percentage point margin on a two-candidate-preferred basis. The two-party result is also known as the swing required for the seat to change hands. Given a uniform swing to the opposition or government parties in an election, the number of seats that change hands can be predicted. Swings are never uniform, but in practice variations of swing among the Australian states usually tend to cancel each other out. Seats are arranged in safeness categories according to the Australian Electoral Commission's (AEC) classification of safeness. "Safe" seats require a swing of over 10 per cent to change, "fairly safe" seats require a swing of between 6 and 10 per cent, while "marginal" seats require a swing of less than 6 per cent. The swings for South Australian and Victorian seats are notional, based on calculations by the AEC.

At the 2016 federal election of the 150 House of Representatives seats the Liberal/National Coalition won 76, a one-seat majority, Labor won 69 seats and crossbenchers won the remaining five. A redistribution in 2017/18 changed the representation entitlements. For the next election, the number of seats in the House will increase to 151, South Australia will lose a seat, Victoria and the Australian Capital Territory (ACT) will gain one seat each.

The following pendulum is known as the Mackerras pendulum, invented by psephologist Malcolm Mackerras. Based upon the outcome of the 2007 federal election and changes before the 2010 election, the pendulum works by lining up all of the seats held in Parliament, 83 Labor, 55 Liberal, 9 National, and 3 independent, according to the percentage point margin on a two party preferred basis.

The Coalition won the 2013 federal election with 90 of 150 lower house seats on a current 17-seat, 3.65-point two-party swing, defeating the 6-year Labor government. Labor holds 55 seats while crossbenchers hold the remaining five. The Division of Fairfax was the last seat to be declared.

This is a Mackerras pendulum for the 2016 Australian federal election.

The Coalition won the 2016 federal election with a one-seat majority 76 of 150 lower house seats. Labor holds 69 seats while crossbenchers hold the remaining five.

The Labor party won the 2018 state election by winning 55 of the 88 lower house seats. The coalition won 27 seats while the Greens and independents won 3 each.

The Coalition won the 2019 federal election with a three-seat majority of 77 of 151 lower house seats. Labor holds 68 seats, and crossbenchers hold the remaining six.

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.

References

  1. Goot M Three strikes against the polls, or the Govt is out ) Australian Broadcasting Corporation, Opinion, 1 October 2007