Two-party-preferred Vote
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Two-party-preferred Vote

Instant-runoff voting method. TPP/TCP vote is calculated when two candidates remain.

In Australian politics, the two-party-preferred vote (TPP or 2PP) is the result of an election or opinion poll after preferences have been distributed to the highest two candidates, who in some cases can be independents. For the purposes of TPP, the Liberal/National Coalition is usually considered a single party, with Labor being the other major party. Typically the TPP is expressed as the percentages of votes attracted by each of the two major parties, e.g. "Coalition 50%, Labor 50%", where the values include both primary votes and preferences. The TPP is an indicator of how much swing has been attained/is required to change the result, taking into consideration preferences, which may have a significant effect on the result.

The TPP assumes a two-party system, i.e. that after distribution of votes from less successful candidates, the two remaining candidates will be from the two major parties. However, in some electorates this is not the case. The two-candidate-preferred vote (TCP) is the result after preferences have been distributed, using instant-runoff voting, to the final two candidates, regardless of which party the candidates represent. For electorates where the two candidates are from the major parties, the TCP is also the TPP. For electorates where these two candidates are not both from the major parties, preferences are notionally distributed to the two major parties to determine the TPP. In this case the TPP differs from the TCP, and is not informative. TPP results above seat-level, such as a national or statewide TPP, are also informative only and have no direct effect on the election outcome.

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. The New South Wales lower house uses optional-preference instant runoff voting - with some votes giving limited or no preferences, TPP/TCP is not as meaningful. TPP/TCP does not occur in the Tasmanian lower house or the Australian Capital Territory due to a different system altogether, the Hare-Clark proportional voting system. Aside from Tasmania, TPP/TCP is not used in any other upper houses in Australia, with most using the group ticket single transferable proportional voting system.[1]


Australia originally used first-past-the-post voting as used by the House of Commons of the United Kingdom. Federal election full-preference instant-runoff voting was introduced by the government of the day after the 1918 Swan by-election, and has been in use ever since. In that by-election, candidates from the Australian Labor Party, the Nationalist Party government (predecessor to the United Australia Party and Liberal Party of Australia), and the emerging National Party of Australia (then Country Party) all received around a third of the vote, however, as Labor had a plurality of three percent, it won the seat. The new system allowed the two non-Labor parties to compete against one another in many seats without risking losing the seat altogether.

The Coalition now includes four parties: the Liberal Party of Australia except Queensland and the Northern Territory, the National Party of Australia in New South Wales and Victoria, the Liberal National Party of Queensland, and the Country Liberal Party in the Northern Territory. It is increasingly uncommon for seats to be contested by more than one Coalition candidate. For example, in the 2010 federal election, only three seats were contested by more than one Coalition candidate. With the popularity of parties such as the Greens and One Nation, preference flows are very significant for all parties in Australia.

Not distributing preferences was historically common in seats where a candidate received over 50 percent of the primary vote. Federal seat and national TPP results have only been produced as far back as 1937, though it was not uncommon in the next few decades for major parties at federal elections to not field a candidate in a few "safe" seats, but since 1972, all seats at federal elections have been contested by the major parties. Full preference distributions have occurred in all seats since 1983.[2]

South Australian state elections have boundaries strategically redrawn before each election with a fairness aim based on the prior election TPP vote, the only state to do so. 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.[3]


Under the full-preference instant-runoff voting system, in each seat, the candidate with the lowest vote is eliminated and their preferences are distributed; this process repeats until only two candidates remain. Whilst every seat has a TCP result, seats where the major parties have come first and second are commonly referred to as having a TPP result. In a TCP contest between Labor and the NSW/Vic Nationals and without a Liberal candidate, this is also considered a TPP, with the Nationals in these states considered a de facto major party within the Liberal/National Coalition. In seats where the major parties do not come first and second, differing TPP and TCP results are returned. When only one of two major parties contest a seat, such as at some by-elections, only a TCP result is produced. Swings in Australian parliaments are more commonly associated with the TPP vote. At the 2013 federal election, 11 of 150 seats returned differing TPP and TCP figures ("non-classic seats"), indicating a considerable two-party system.[4]

The tallying of seat TPP results gives a statewide and/or national TPP vote. Non-classic seats have votes redistributed for informational purposes to the major parties so that every seat has a TPP result. 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. Several federal elections since 1937 have seen a government elected with a minority of the TPP vote: 1940 (49.7%), 1954 (49.3%), 1961 (49.5%), 1969 (49.8%), 1990 (49.9%) and 1998 (49.0%).

As the TPP vote rather than the primary vote is a better indicator of who is in front with seats won and lost on a preferential basis, Australian opinion polls survey voter intention with a TPP always produced. However, these TPP figures tend to be calculated based on preference flows at the previous election rather than asked at the time of polling. The difference between the two is usually within the margin of error (usually +/- 3 percentage points). History has shown that prior-election preference flows are more reliable.[5]


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. Such an exercise is shown for the 2017 by-election in Bennelong:

2017 Bennelong by-election - Preference Flow Data[6]
Party Candidate First preferences % preference to
Votes % Liberal Labor
  Greens Justin Alick 5,688 6.8 19.7 80.3
  Conservatives Joram Richa 3,609 4.3 86.5 13.5
  Christian Democrats Gui Dong Cao 2,626 3.1 72.4 27.6
  Science James Jansson 1,041 1.2 39.4 60.6
  Sustainable Australia Wesley Folitarik 995 1.2 48.9 51.1
  Affordable Housing Anthony Ziebell 741 0.9 44.7 55.3
  Liberty Alliance Tony Robinson 719 0.9 79.0 21.0
  Progressives Chris Golding 425 0.5 42.1 57.9
  People's Party James Platter 186 0.2 48.9 51.1
  Non-Custodial Parents Anthony Fels 132 0.2 56.1 43.9
Totals 16,162 19.2 51.2 48.8

Preference Flows in Federal Elections

2019 Australian federal election - Preference Flow Data[7]
Party First preferences % preference to
Votes % Liberal Labor
  Greens 1,482,923 10.40 17.8 82.2
  United Australia Party 488,817 3.43 65.1 34.9
  Independent 479,836 3.37 40.6 59.4
  One Nation 438,587 3.08 65.2 34.8
  Christian Democrat 116,675 0.68 74.4 25.6
  Conservative Nationals 77,203 0.54 71.8 28.2
  Katter's Australia 69,736 0.49 67.0 33.0
  Centre Alliance 46,931 0.33 32.9 67.1
  Shooters, Fishers, Farmers 41,479 0.29 59.1 40.9
  Sustainable Australia 35,618 0.25 46.0 54.0
  Liberal Democrats 34,666 0.24 77.2 22.8
  Justice 26,803 0.19 46.2 53.8
  Western Australia 25,298 0.18 49.0 51.0
  Australian Christians 23,802 0.17 80.8 19.2
  Democratic Labour 18,287 0.13 39.8 60.2
  Rise Up Australia 18,287 0.10 60.4 39.6
  Science 12,617 0.09 32.5 67.5
  Victorian Socialists 12,453 0.09 12.4 87.6
  Reason 8,895 0.06 31.2 68.8
  Progressives 7,759 0.05 32.8 67.2
  Australia First 6,786 0.05 56.4 43.6
  Great Australian 5,355 0.04 53.1 46.9
  CEC 3,267 0.02 26.4 73.6
  Socialist Equality 2,866 0.02 36.9 63.1
  Socialist Alliance 2,447 0.02 20.2 79.8
  Non-Affiliated 2,143 0.02 32.4 67.6
  Better Families 2,072 0.01 64.1 35.9
  Australian Democrats 2,039 0.01 30.9 69.1
  Workers 1,676 0.01 58.7 41.3
  Love Australia or Leave 1,564 0.01 54.5 45.5
  Child Protection 1,219 0.01 45.4 54.6
  Non-Custodial Parents 1,213 0.01 51.3 48.7
  Involuntary Medication Objectors 1,179 0.01 36.4 63.6
  Flux 602 0.00 46.2 53.8


Federal, Swan 1918

1918 Swan by-election: Division of Swan, Western Australia
Party Candidate Votes % ±%
Labor Edwin Corboy 6,540 34.4 N/A
Country Basil Murray 5,975 31.4 N/A
Nationalist William Hedges 5,635 29.6 N/A
Independent William Watson 884 4.6 N/A
Turnout 19,213 64.3%
Labor gain from Nationalist Swing N/A

The result of the 1918 Swan by-election, the first-past-the-post election which caused the government of the day to introduce full-preference instant-runoff voting, under which Labor would have been easily defeated. Labor won the seat, and their majority was 3.0 points (34.4 minus 31.4). No swings are available as the Nationalists retained the seat unopposed at the previous election.

Federal, Adelaide 2004

2004 Australian federal election: Division of Adelaide, South Australia
Party Candidate Votes % ±%
Liberal Trish Worth 38,530 45.29 +0.82
Labor Kate Ellis 35,666 41.92 +5.50
Greens Jake Bugden 6,794 7.99 +2.02
Family First Peter G Robins 1,753 2.06 +2.06
Democrats Richard Pascoe 1,355 1.59 -9.30
Independent Amanda Barlow 978 1.15 +1.15
Total formal votes 85,076 95.60 +0.66
Informal votes 3,920 4.40 -0.66
Turnout 88,996 93.62 -1.09
Two-party-preferred result
Labor Kate Ellis 43,671 51.33 +1.95
Liberal Trish Worth 41,405 48.67 -1.95
Labor gain from Liberal Swing +1.95

It can be seen that the Liberal candidate had a primary vote lead over the Labor candidate. In a first-past-the-post vote, the Liberals would have retained the seat, and their majority would be said to be 3.4 points (45.3 minus 41.9).

However, under full-preference instant-runoff voting, the votes of all the minor candidates were distributed as follows:

2nd count: Barlow 978 votes distributed
Party Candidate Added votes % Votes %
Liberal Trish Worth 172 17.6 38,702 45.5
Labor Kate Ellis 206 21.1 35,872 42.2
Greens Jake Bugden 365 37.3 7,159 8.4
Family First Peter G Robins 96 9.8 1,849 2.2
Democrats Richard Pascoe 139 14.2 1,494 1.8
Total 978 85,076
3rd count: Democrats 1,494 votes distributed
Party Candidate Added votes % Votes %
Liberal Trish Worth 343 23.0 39,045 45.9
Labor Kate Ellis 494 33.1 36,366 42.8
Greens Jake Bugden 560 37.5 7,719 9.1
Family First Peter G Robins 97 6.5 1,946 2.3
Total 1,494 85,076
4th count: Family First 1,946 votes distributed
Party Candidate Added votes % Votes %
Liberal Trish Worth 1,098 56.4 40,143 47.2
Labor Kate Ellis 377 19.4 36,743 43.2
Greens Jake Bugden 471 24.2 8,190 9.6
Total 1,946 85,076
5th count: Greens 8,190 votes distributed - final TPP/TCP
Party Candidate Added votes % Votes %
Labor Kate Ellis 6,928 84.6 43,671 51.3
Liberal Trish Worth 1,262 15.4 41,405 48.7
Total 8,190 85,076 1.3

The process of allocating the votes can be more succinctly shown thus:

2004 Australian federal election: Division of Adelaide, South Australia
Allocation of votes by count
Party Candidate Count
1st 2nd 3rd 4th 5th Total
  Labor Kate Ellis 35,666 206 494 377 6,928 43,671
  Liberal Trish Worth 38,530 172 343 1,098 1,262 41,405
  Greens Jake Bugden 6,794 365 560 471 (8,190)  
  Family First Peter G Robins 1,753 96 97 (1,946)    
  Democrats Richard Pascoe 1,355 139 (1,494)      
  Independent Amanda Barlow 978 (978)        

Thus, Labor defeated the Liberals, with 85 percent of Green and Green-preferenced voters preferencing Labor on the last distribution. Labor's TPP/TCP vote was 51.3 percent, a TPP/TCP majority of 1.3 points, and a TPP/TCP swing of 1.9 points compared with the previous election.

South Australia, Frome 2009

2009 Frome state by-election: Electoral district of Frome, South Australia[8][9]
Party Candidate Votes % ±%
Liberal Terry Boylan 7,576 39.24 -8.86
Labor John Rohde 5,041 26.11 -14.93
Independent Geoff Brock 4,557 23.60 +23.60
National Neville Wilson 1,267 6.56 +6.56
Greens Joy O'Brien 734 3.80 +0.06
One Nation Peter Fitzpatrick 134 0.69 +0.69
Total formal votes 19,309 97.12 +0.21
Informal votes 573 2.88 -0.21
Turnout 19,882 89.79 -4.44
Two-party-preferred result
Liberal Terry Boylan 9,976 51.67 -1.74
Labor John Rohde 9,333 48.33 +1.74
Two-candidate-preferred result
Independent Geoff Brock 9,987 51.72 +51.72
Liberal Terry Boylan 9,322 48.28 -5.13
Independent gain from Liberal Swing N/A

The 2009 Frome by-election was closely contested, with the result being uncertain for over a week.[10][11][12] Liberal leader Martin Hamilton-Smith claimed victory on behalf of the party.[13][14][15] The result hinged on the performance of Brock against Labor in the competition for second place. Brock polled best in the Port Pirie area, and received enough eliminated candidate preferences to end up ahead of the Labor candidate by 30 votes.

Distribution of Preferences - 4th count[16]
Party Candidate Votes % ±%
Liberal Terry Boylan 8,215 42.54
Independent Geoff Brock 5,562 28.81
Labor John Rohde 5,532 28.65

Brock received 80 percent of Labor's fifth count preferences to achieve a TCP vote of 51.72 percent (a majority of 665 votes) against the Liberal candidate.[17][18] The by-election saw a rare TPP swing to an incumbent government, and was the first time an opposition had lost a seat at a by-election in South Australia.[19][20] The result in Frome at the 2010 state election saw Brock come first on primary votes, increasing his primary vote by 14.1 points to a total of 37.7 percent and his TCP vote by 6.5 points to a total of 58.2 percent. Despite a statewide swing against Labor at the election, Labor again increased its TPP vote in Frome by 1.8 points to a total of 50.1 percent.

Federal, Melbourne 2010

2010 Australian federal election: Division of Melbourne, Victoria
Party Candidate Votes % ±%
Labor Cath Bowtell 34,022 38.09 -11.42
Greens Adam Bandt 32,308 36.17 +13.37
Liberal Simon Olsen 18,760 21.00 -2.49
Sex Party Joel Murray 1,633 1.83 +1.83
Family First Georgia Pearson 1,389 1.55 +0.55
Secular Penelope Green 613 0.69 +0.69
Democrats David Collyer 602 0.67 -0.76
Total formal votes 89,327 96.38 -0.82
Informal votes 3,356 3.62 +0.82
Turnout 92,683 90.09 -1.41
Two-party-preferred result
Labor Cath Bowtell 65,473 73.30 +1.03
Liberal Simon Olsen 23,854 26.70 -1.03
Two-candidate-preferred result
Greens Adam Bandt 50,059 56.04 +10.75
Labor Cath Bowtell 39,268 43.96 -10.75
Greens gain from Labor Swing +10.75

In this example, the two remaining candidates/parties, one a minor party, were the same after preference distribution at both this election and the previous election. Therefore, differing TPP and TCP votes, margins, and swings resulted.[21]

South Australia, Port Adelaide 2012

2012 Port Adelaide state by-election: Electoral district of Pt Adelaide, South Australia
Party Candidate Votes % ±%
Labor Susan Close 8,218 42.3 -7.6
Independent Gary Johanson 4,717 24.3 +24.3
Independent Sue Lawrie 2,938 15.1 +15.1
Liberal Democrats Stephen Humble 1,415 7.3 +7.3
Greens Justin McArthur 1,096 5.6 -0.6
Independent Colin Thomas 314 1.6 +1.6
Independent Bob Briton 292 1.5 +1.5
One Nation Grant Carlin 269 1.4 +1.4
Democratic Labor Elizabeth Pistor 151 0.8 +0.8
Total formal votes 19,410 92.8 -3.8
Informal votes 1,505 7.2 +3.8
Turnout 20,915 82.8 -10.4
Two-candidate-preferred result
Labor Susan Close 10,277 52.9 -9.8
Independent Gary Johanson 9,133 47.1 +47.1
Labor hold Swing N/A

At the 2012 Port Adelaide state by-election, only a TCP could be produced, as the Liberal Party of Australia (and Family First Party and independent candidate Max James), who contested the previous election and gained a primary vote of 26.8 percent (and 5.9 percent, and 11.0 percent respectively), did not contest the by-election. On a TPP margin of 12.8 points from the 2010 election, considered a safe margin on the current pendulum, Labor would probably have retained their TPP margin based on unchanged statewide Newspoll since the previous election. Labor retained the seat on a 52.9 percent TCP against Johanson after the distribution of preferences.[22][23][24]

Unlike previous examples, neither a TPP or TCP swing can be produced, as the 2010 result was between Labor and Liberal rather than Labor and independent with no Liberal candidate. An increase or decrease in margins in these situations cannot be meaningfully interpreted as swings. As explained by the ABC's Antony Green, when a major party does not contest a by-election, preferences from independents or minor parties that would normally flow to both major parties does not take place, causing asymmetric preference flows. Examples of this are the 2008 Mayo and 2002 Cunningham federal by-elections, with seats returning to TPP form at the next election.[25] This contradicts News Ltd claims of large swings and a potential Liberal Party win in Port Adelaide at the next election.[26][27]

House of Representatives primary, two-party and seat results

A two-party system has existed in the Australian House of Representatives since the two non-Labor parties merged in 1909.[] The 1910 election was the first to elect a majority government, with the Australian Labor Party concurrently winning the first Senate majority. Prior to 1909 a three-party system existed in the chamber. A two-party-preferred vote (2PP) has been calculated since the 1919 change from first-past-the-post to preferential voting and subsequent introduction of the Coalition. ALP = Australian Labor Party, L+NP = grouping of Liberal/National/LNP/CLP Coalition parties (and predecessors), Oth = other parties and independents.

See also


  1. ^ "How the House of Representatives votes are counted". Australian Electoral Commission. Retrieved 2012.
  2. ^ "Historical national and state-by-state two-party preferred results". Australian Electoral Commission. 17 February 2016. Retrieved 2016.
  3. ^ Malcolm Mackerras. "The Results and the Pendulum". Australian National University. Retrieved 2016.
  4. ^ "Non-classic divisions, 2010 federal election". Australian Electoral Commission. 4 November 2013. Retrieved 2016.
  5. ^ Antony Green (10 February 2012). "How Should Reachtel's Ashgrove Polls be Interpreted". Retrieved 2016.
  6. ^ Green, Anthony (15 January 2018). "2017 Bennelong by-election: Commentary". ABC News.
  7. ^ Green, Antony. "Preference Flows at the 2019 Federal Election - Antony Green's Election Blog". Retrieved 2020.
  8. ^ "2009 Frome by-election results: State Electoral Office". Archived from the original on 20 January 2009. Retrieved 2010.
  9. ^ "2009 Frome By-election: ABC Elections". 2 February 2009. Retrieved 2010.
  10. ^ "Frome by-election goes down to the wire". ABC Online. 18 January 2009. Retrieved 2009.
  11. ^ Green, Antony. "Frome By-election Results". ABC Online. Retrieved 2009.
  12. ^ Emmerson, Russell; Pepper, Chris (18 January 2009). "Liberals confident they'll hold Outback seat of Frome". The Advertiser. Archived from the original on 20 January 2009. Retrieved 2009.
  13. ^ "Liberals claim victory in Frome". Poll Bludger (Crikey). 21 January 2009. Archived from the original on 31 January 2009. Retrieved 2009. This article reproduces the original Liberal press release, no longer available on the SA Liberal site.
  14. ^ Hendrik Gout (30 January 2009). "Frome one loss to another: Independent Weekly 30/1/2009". Retrieved 2010.
  15. ^ Richardson, Tom (30 January 2009). "Frome, a lost moment for the Libs: Independent Weekly 30/1/2009". Retrieved 2010.
  16. ^ "District of Frome" (PDF). Retrieved 2010.[permanent dead link]
  17. ^ Pepper, Chris (25 January 2009). "Shock Frome loss rocks SA Liberals". The Advertiser. Retrieved 2009.
  18. ^ Jamie Walker (31 January 2009). "Peace plea as Nationals take revenge on Liberals at polling booth: The Australian 31/1/2009". Archived from the original on 6 March 2009. Retrieved 2010.
  19. ^ David Nason, New York correspondent (26 January 2009). "Leader left with pumpkin: The Australian 26/1/2009". Archived from the original on 11 September 2012. Retrieved 2010.
  20. ^ Gavin Lower and David Nason (26 January 2009). "Libs demand recount after shock poll loss: The Australian 26/1/2009". Archived from the original on 13 September 2012. Retrieved 2010.
  21. ^ "Melbourne 2010 election result". Australian Electoral Commission. 29 September 2010. Retrieved 2016.
  22. ^ "2012 Port Adelaide by-election results: ECSA". Archived from the original on 28 July 2012.
  23. ^ "Port Adelaide by-election preference distribution: ECSA" (PDF). Archived from the original (PDF) on 9 April 2013.
  24. ^ Antony Green (20 February 2012). "2012 Port Adelaide by-election results". Retrieved 2016.
  25. ^ Antony Green (13 February 2012). "A Comment on the Size of the Port Adelaide Swing". Retrieved 2016.
  26. ^ "Port now a poll target for Liberals". The Advertiser. 2 March 2012. Retrieved 2016.
  27. ^ "Susan Close wins Port Adelaide for Labor but seat now marginal". The Australian. 11 February 2012.
    "Labor Keeps Port Adelaide, Ramsay in South Australian by-elections". The Australian. 12 February 2012.
    "By-election swings carry 'message for Labor'". The Australian. 13 February 2012.

External links

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