Two-party-preferred vote
In Australian politics, the two-party-preferred vote (TPP or 2PP), commonly referred to as simply preferences, is the result of an election or opinion poll after preferences have been distributed to the two candidates with the highest number of votes who, in some cases, can be independents.
The full allocation of preferences under instant-runoff voting is used in the lower houses of the Federal, Queensland, Victorian, Western Australian, South Australian, and Northern Territory parliaments, as well as the upper house of Tasmania.
Aside from Tasmania, TPP/TCP is not used in any other upper houses in Australia, with most using the proportional single transferable vote system.
Federal election full-preference instant-runoff voting was introduced after the 1918 Swan by-election, and has been in use ever since.
Not distributing preferences was historically common in seats where a candidate received over 50 percent of the primary vote.
The culmination of the historical state lower house seat malapportionment known as the Playmander eventually saw it legislated after 1989 that the Electoral Commission of South Australia redraw boundaries after each election with the objective of the party that receives over 50 percent of the TPP vote at each forthcoming election forms government.
Nationally in 1983/84, minor gerrymandering by incumbent federal governments was legislated against with the formation of the independent Commonwealth statutory authority, the Australian Electoral Commission.
In seats where the major parties do not come first and second, differing TPP and TCP results are returned.
Whilst the TCP is the determining factor in deciding which candidate wins a seat, the overall election TPP is statistical and indicative only, as swings in seats are not uniform, and a varying range of factors can influence marginal-seat wins with single-member electorates.
However, these TPP figures tend to be calculated based on preference flows at the previous election rather than asked at the time of polling.
Early examples of this included Maiwar at the 2017 Queensland State Election, in which the Green candidate came third on the primary vote, but earned enough preferences to make it into the top two, and win the seat based on Labor preferences, who were initially second place.
At the 2022 Federal Election, the AEC performed three candidate counts for the first time in the seats of Macnamara, and Brisbane, which fulfilled the latter and former criteria respectively.
[6] After the count has taken place, it is possible to analyze the ultimate preference flows for votes cast for the parties that were ultimately excluded from the TPP calculation, in order to determine if the composite flow would have significantly affected the final result.
Examples of this are the 2008 Mayo and 2002 Cunningham federal by-elections, with seats returning to TPP form at the next election.
[26] This contradicts News Ltd claims of large swings and a potential Liberal Party win in Port Adelaide at the next election.
[27][28] A two-party system has existed in the Australian House of Representatives since the two non-Labor parties merged in 1909.
In 2019, the Greens also finished second for the first time in the Melbourne seat of Kooyong, which was held by the Liberals until 2022, when it was won by teal independent Monique Ryan.
In 2016, the Nick Xenophon Team (NXT) finished second in three South Australian electorates: Barker, Grey and Port Adelaide (the latter of which has since been abolished).
[29] At the previous state election in 2019, the Greens finished second in four seats (Davidson, Manly, Pittwater and Vaucluse), all of which were won by the Liberals and were all located in Sydney.
