Two-party-preferred vote

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

In Australian politics the two-party-preferred vote (TPP) is the result of an election or opinion poll after preferences have been distributed to the last two parties. 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 55%, Labor 45%", 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 these 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 informative but has no effect on the election outcome. TPP results above seat-level, such as a national or state-wide TPP, are also informative only and has no result on the election outcome.

The full allocation of preferences under instant-runoff voting is used in the lower houses of the Federal, Victorian, Western Australian, South Australian, and Northern Territory parliaments, as well as the upper house of Tasmania. The New South Wales lower house and Queensland use 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]

History[edit]

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 has been in existence since its introduction by the government after the 1918 Swan 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 Labor remained a few percent in front of both other candidates to win the seat. The system has allowed the two non-Labor parties to compete in many seats without splitting the conservative vote in three-cornered-contests. Even in landslide conservative election wins such as 1975 or 1996, Labor had the largest primary vote. The Coalition now comprises 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, by 2010 only three seats were contested by more than one Coalition candidate, all in New South Wales. Four seats were contested by the non-Coalition National Party of Western Australia, none were contested by the non-Coalition National Party of South Australia, and neither are automatically part of the Coalition TPP. Preferences have also been of significant relevance to the DLP, the Democrats, One Nation, the Greens, and independents.

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]

Procedure[edit]

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. 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 state-wide 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 prior election rather than asked at the time of polling. There difference between the two is usually within the margin of error (usually +/- 3 percent). History has shown that prior election preference flows are more reliable.[5]

Examples[edit]

Federal, Swan 1918[edit]

Swan by-election, 1918: 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 percentage points (34.4 minus 31.4). No swings are available as the Nationalists retained the seat unopposed at the previous election.

Federal, Adelaide 2004[edit]

Australian federal election, 2004: 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 percentage 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

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 percent compared with the previous election.

South Australia, Frome 2009[edit]

Frome state by-election, 2009: Electoral district of Frome, South Australia[6][7]
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
Nationals SA Neville Wilson 1,267 6.56 +6.56
SA 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.[8][9][10] Liberal leader Martin Hamilton-Smith claimed victory on behalf of the party.[11][12][13] 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[14]
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.[15][16] 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.[17][18] The result in Frome at the 2010 state election saw Brock come first on primary votes, increasing his primary vote by 14.1 percent to a total of 37.7 percent and his TCP vote by 6.5 percent 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 percent to a total of 50.1 percent.

Federal, Melbourne 2010[edit]

Australian federal election, 2010: 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.[19]

South Australia, Port Adelaide 2012[edit]

Pt Adelaide state by-election, 2012: Electoral district of Pt Adelaide, South Australia
Party Candidate Votes % ±%
Labor Susan Close 8,218 42.3 –7.6
Independent for You Gary Johanson 4,717 24.3 +24.3
Independent True Blue Voice Sue Lawrie 2,938 15.1 +15.1
Liberal Democrats Stephen Humble 1,415 7.3 +7.3
SA Greens Justin McArthur 1,096 5.6 –0.6
Independent Ban Live Animal Exports Colin Thomas 314 1.6 +1.6
Independent Communist Australia 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 for You 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.[20][21][22]

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.[23] This contradicts News Ltd claims of large swings and a potential Liberal Party win in Port Adelaide at the next election.[24][25]

Federal results since 1937[edit]

ALP = Australian Labor Party, L+NP = grouping of Liberal/National/LNP/CLP Coalition Parties (and predecessors), Oth = other parties and independents.

House of Representatives results and polling
Primary vote TPP vote Seats
ALP L+NP Oth. ALP L+NP ALP L+NP Oth. Total
7 Sep 2013 election 33.4% 45.6% 21.1% 46.5% 53.5% 55 90 5 150
3–5 Sep 2013 poll 33% 46% 21% 46% 54%
21 Aug 2010 election 38.0% 43.3% 18.8% 50.1% 49.9% 72 72 6 150
17–19 Aug 2010 poll 36.2% 43.4% 20.4% 50.2% 49.8%
24 Nov 2007 election 43.4% 42.1% 14.5% 52.7% 47.3% 83 65 2 150
20–22 Nov 2007 poll 44% 43% 13% 52% 48%
9 Oct 2004 election 37.6% 46.7% 15.7% 47.3% 52.7% 60 87 3 150
6–7 Oct 2004 poll 39% 45% 16% 50% 50%
10 Nov 2001 election 37.8% 43.0% 19.2% 49.0% 51.0% 65 82 3 150
7–8 Nov 2001 poll 38.5% 46% 15.5% 47% 53%
3 Oct 1998 election 40.1% 39.5% 20.4% 51.0% 49.0% 67 80 1 148
30 Sep–1 Oct 1998 poll 44% 40% 16% 53% 47%
2 Mar 1996 election 38.7% 47.3% 14.0% 46.4% 53.6% 49 94 5 148
28–29 Feb 1996 poll 40.5% 48% 11.5% 46.5% 53.5%
13 Mar 1993 election 44.9% 44.3% 10.7% 51.4% 48.6% 80 65 2 147
11 Mar 1993 poll 44% 45% 11% 49.5% 50.5%
24 Mar 1990 election 39.4% 43.5% 17.1% 49.9% 50.1% 78 69 1 148
11 Jul 1987 election 45.8% 46.1% 8.1% 50.8% 49.2% 86 62 0 148
1 Dec 1984 election 47.6% 45.0% 7.4% 51.8% 48.2% 82 66 0 148
5 Mar 1983 election 49.5% 43.6% 6.9% 53.2% 46.8% 75 50 0 125
18 Oct 1980 election 45.2% 46.3% 8.5% 49.6% 50.4% 51 74 0 125
10 Dec 1977 election 39.7% 48.1% 12.2% 45.4% 54.6% 38 86 0 124
13 Dec 1975 election 42.8% 53.1% 4.1% 44.3% 55.7% 36 91 0 127
18 May 1974 election 49.3% 44.9% 5.8% 51.7% 48.3% 66 61 0 127
2 Dec 1972 election 49.6% 41.5% 8.9% 52.7% 47.3% 67 58 0 125
25 Oct 1969 election 47.0% 43.3% 9.7% 50.2% 49.8% 59 66 0 125
26 Nov 1966 election 40.0% 50.0% 10.0% 43.1% 56.9% 41 82 1 124
30 Nov 1963 election 45.5% 46.0% 8.5% 47.4% 52.6% 50 72 0 122
9 Dec 1961 election 47.9% 42.1% 10.0% 50.5% 49.5% 60 62 0 122
22 Nov 1958 election 42.8% 46.6% 10.6% 45.9% 54.1% 45 77 0 122
10 Dec 1955 election 44.6% 47.6% 7.8% 45.8% 54.2% 47 75 0 122
29 May 1954 election 50.0% 46.8% 3.2% 50.7% 49.3% 57 64 0 121
28 Apr 1951 election 47.6% 50.3% 2.1% 49.3% 50.7% 52 69 0 121
10 Dec 1949 election 46.0% 50.3% 3.7% 49.0% 51.0% 47 74 0 121
28 Sep 1946 election 49.7% 39.3% 11.0% 54.1% 45.9% 43 26 5 74
21 Aug 1943 election 49.9% 23.0% 27.1% 58.2% 41.8% 49 19 6 74
21 Sep 1940 election 40.2% 43.9% 15.9% 50.3% 49.7% 32 36 6 74
23 Oct 1937 election 43.2% 49.3% 7.5% 49.4% 50.6% 29 44 2 74
Polling conducted by Newspoll and published in The Australian. Three percent margin of error.


See also[edit]

External links[edit]

References[edit]

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