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 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 45%, Labor 55%", 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 statewide 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.

History

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.

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.

Procedure

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.

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 prior election rather than asked at the time of polling. There 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.

Examples

Federal, Swan 1918

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 points (34.4 minus 31.4). No swings are available as the Nationalists retained the seat unopposed at the previous election.

Federal, Adelaide 2004

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 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 points compared with the previous election.

South Australia, Frome 2009

Frome state by-election, 2009: Electoral district of Frome, South Australia

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. Liberal leader Martin Hamilton-Smith claimed victory on behalf of the party. 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

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. 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. 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

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.

South Australia, Port Adelaide 2012

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.

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

Federal results since 1937

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 September 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 August 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 November 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 October 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 November 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 October 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 March 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 March 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 March 1990 election	39.4%	43.5%	17.1%	49.9%	50.1%	78	69	1	148
11 July 1987 election	45.8%	46.1%	8.1%	50.8%	49.2%	86	62	0	148
1 December 1984 election	47.6%	45.0%	7.4%	51.8%	48.2%	82	66	0	148
5 March 1983 election	49.5%	43.6%	6.9%	53.2%	46.8%	75	50	0	125
18 October 1980 election	45.2%	46.3%	8.5%	49.6%	50.4%	51	74	0	125
10 December 1977 election	39.7%	48.1%	12.2%	45.4%	54.6%	38	86	0	124
13 December 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 December 1972 election	49.6%	41.5%	8.9%	52.7%	47.3%	67	58	0	125
25 October 1969 election	47.0%	43.3%	9.7%	50.2%	49.8%	59	66	0	125
26 November 1966 election	40.0%	50.0%	10.0%	43.1%	56.9%	41	82	1	124
30 November 1963 election	45.5%	46.0%	8.5%	47.4%	52.6%	50	72	0	122
9 December 1961 election	47.9%	42.1%	10.0%	50.5%	49.5%	60	62	0	122
22 November 1958 election	42.8%	46.6%	10.6%	45.9%	54.1%	45	77	0	122
10 December 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 April 1951 election	47.6%	50.3%	2.1%	49.3%	50.7%	52	69	0	121
10 December 1949 election	46.0%	50.3%	3.7%	49.0%	51.0%	47	74	0	121
28 September 1946 election	49.7%	39.3%	11.0%	54.1%	45.9%	43	26	5	74
21 August 1943 election	49.9%	23.0%	27.1%	58.2%	41.8%	49	19	6	74
21 September 1940 election	40.2%	43.9%	15.9%	50.3%	49.7%	32	36	6	74
23 October 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-point margin of error.

See also

• Swing (Australian politics)
• Mackerras Pendulum

External links

• National and state-by-state TPP results since 1949 – Australian Electoral Commission
• National TPP results since 1937 – Malcolm Mackerras