Draft:Multi-round voting

• Comment: Almost entirely unsourced Mattdaviesfsic (talk) 06:40, 13 January 2023 (UTC)

Multi-round voting, also sometimes referred to as runoff voting is a type of voting method in which voters participate in successive polls in one election, usually until a candidate or a group of candidates receives an absolute majority of votes^[1] (or another prescribed percentage). Later rounds are typically only held if no candidate fulfills conditions of victory in the first round - an exception is when the first round is a primary election, in which case a general election is always held afterwards.

Multi-round voting may be used to elect a single winner (many countries elect their presidents in this way) or more than one winners (for example, the European Parlament elects its vice-presidents in this way). In single winner systems, voters usually may cast a single vote for their most preferred candidate, meaning the earlier polls basically use the single non-transferable vote system, while the last round uses first-past-the-post voting, but since most commonly only two candidates are on the ballot in this round, one will receive more than 50% of votes (except for a tie).

The most common multi-round system is two-round system (also called runoff voting).

Multi-round systems may have a prescribed number of rounds with certain thresholds to meet to win, which may vary:

• Some systems allow for a candidate to win in the first round of voting with less than 50% of votes, for example, 40% might be enough and/or it might be prescribed that they have to have a lead of at least some (e.g. 10%) percentage over the second place candidate. An example is the election of the President of Argentina.
• Other systems prescribe a larger than 50% majority, i.e. a supermajority. This is typically used to elect heads of state in republican countries where the legislature, not the people elects the head of state. This means a larger consensus is needed to elect any candidate. This requirement is often dropped in later rounds to prevent deadlock. An example is the election of the President of Albania.
• The exhaustive ballot means voting continues for an indeterminate amount of rounds (at most, how many candidates there are, if only 50% is required) with candidates eliminated one by one, until someone is elected.
• Additional requirements may be a minimum turnout threshold for the vote or the majority requirement fixed to the entire electorate as opposed to only the voters.

Instant-runoff voting (IRV) (also known as preferential voting or ranked-choice voting) like the exhaustive ballot involves multiple reiterative counts in which the candidate with fewest votes is eliminated each time. Whilst the exhaustive ballot and the two-round system both involve voters casting a separate vote in each round, under instant-runoff, voters vote only once. This is possible because, rather than voting for only a single candidate, the voter ranks all of the candidates in order of preference. These preferences are then used to transfer the votes of those whose first preference has been eliminated during the course of the count. Because the two-round system and the exhaustive ballot involve separate rounds of voting, voters can use the results of one round to decide how they will vote in the next, whereas this is not possible under IRV. Because it is necessary only to vote once, IRV, like the two-round system, is used for large-scale elections in many places such as Australian general and state elections. IRV often elects a different winner than the two-round system and tends to produce the same results as the exhaustive ballot.

Variants of instant-runoff voting can be designed to reflect the same rules as a two-round voting system. If no single candidate has an absolute majority of votes then only the two highest polling candidates progress to the second count, while all other candidates are excluded and their votes redistributed according to the recorded preferences for continuing candidates. One variant that works this way is called the Contingent vote, detailed below.

In Australia it is called preferential voting and is used to elect members of, among other bodies, the House of Representatives and the Senate. In Ireland it is known as single transferable vote and is used for presidential elections and parliamentary elections.

In the United States, the Louisiana primary, introduced in Louisiana for partisan state elections in 1975 and federal elections in 1978 (with a brief return using a closed primary system in 2010), is virtually identical to the two-round system. Instead of the standard American system of primary elections to choose each party's candidate, followed by a general election contest between the winners of the primaries, the Louisiana primary allows voters to select any candidate, regardless of party affiliation. If one candidate receives an absolute majority of the votes cast, he or she is declared the winner. Otherwise, the two highest vote-winners in the first round—in effect, the first round of a two-round system—are then the only candidates whose names appear on the ballot at a runoff election, effectively requiring one candidate to win an absolute majority to take office. The key difference between the Louisiana primary and a typical two-round system is that political parties do not select the individuals using their party labels; rather, candidates can self-identify using the label of their preferred political party (or no party at all).

The state of Washington adopted a system similar to Louisiana's in 2008, which came into effect in 2010 after legal difficulties. California approved a similar system in 2010, coming into effect for the 36th congressional district election in February 2011. The system used in Washington and California is referred to as the nonpartisan blanket primary or top-two primary system. Like the Louisiana primary, candidates self-select their party label on the ballot rather than being nominated by a particular political party.

The main difference between a nonpartisan blanket primary and either a standard two-round system or the Louisiana primary is that a second round of voting is required, even if a candidate wins an absolute majority of votes in the primary.

• Ranked voting systems
• List of electoral systems by country
• Top-four primary

• A Handbook of Electoral System Design from International IDEA
• Electoral Design Reference from the ACE Project