Two-party-preferred vote

In Australian politics, the two-party-preferred vote (TPP or 2PP), is the result of an opinion poll or a projection of an election result where preferences are distributed to one of the two major parties, the Labor Party and the Liberal/National Coalition e.g. "Coalition 50%, Labor 50%. The preference distribution is usually based upon the results of the last election, and the votes for other candidates are distributed between to the two parties.

As such the TPP is a rough indicator of voting intent that focuses on determining the likely majority in the lower house. It is compared to previous values to predict the swing and hence the likelihood of a change in government between the major parties.

The TPP assumes a two-party system of government, i.e. that after distribution of votes from less successful candidates, the two remaining candidates will be from each of the two major parties. It provides no indication of the number of representatives of other parties or independent views on the cross-bench, and as the proportion of votes for other candidates increases the TPP becomes less useful. It cannot predict a hung parliament as it does not quantify the alternatives to the two parties.

The TPP is often confused with the two-candidate-preferred vote (TCP). The TCP is the electoral penultimate result for an electoral division where preferences have been distributed using instant-runoff voting. The winner of the contest is the candidate with over 50% of the TCP vote.

Unlike the TCP, the TPP is informative only and has no direct effect on the election outcome. It is an indicator used for analysing results above seat-level, such as a national or statewide TPP. For seats the TCP is the preferred indicator, because when the final two candidates are from the major parties, the TCP will have the same value as the TPP, and when at least one of the final candidates is not from a major party the TPP is misleading, not informative.

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 single transferable vote system. Aside from Tasmania, TPP/TCP is not used in any other upper houses in Australia, with most using the proportional single transferable vote system.

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 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.

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.