History and use of instant-runoff voting

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Instant-runoff voting (IRV) is a ranked voting method used in elections with a single winner. It’s also called the Alternative Vote (AV) or ranked-choice voting in different places. Voters order candidates by preference (1st, 2nd, 3rd, and so on).

How it works:
- Each voter marks their preferences.
- First, all the 1st choices are counted. If someone has more than half of the first-choice votes, that person wins.
- If no one has a majority, the candidate with the fewest first-choice votes is eliminated. The ballots for that candidate are redistributed to the remaining candidates based on the voters’ next preferences.
- The process repeats, eliminating the lowest and transferring votes, until one candidate earns a majority. The final result often resembles a two-candidate race known as the two-party preferred outcome.

IRV is used when there is one winner. It is related to the Single Transferable Vote (STV), which is used for multi-seat elections; IRV is the single-winner version of that idea.

A brief history:
- IRV grew out of earlier ranked voting methods. In the early 1900s, places in Australia and elsewhere tried different contingent or preferential schemes.
- Australia adopted IRV for the federal House of Representatives in 1918, and later for many state elections; Queensland was the last Australian state to switch to AV in 1962.
- In other countries, IRV is known as the Alternative Vote or preferential voting. Ireland uses STV for most elections, but single-winner Irish races use IRV. India uses a form of IRV for selecting presidents.
- IRV has been used in various forms around the world, including Fiji and Papua New Guinea in some elections.

In the United States, IRV has been adopted by many cities for local offices (such as San Francisco, Minneapolis, Oakland, Cambridge, and others). Maine became the first state to use IRV for statewide elections in 2018 for some offices, and Alaska began using it for state and federal general elections in 2020. The United Kingdom has discussed IRV as a nationwide option, but a 2011 referendum rejected adopting it for Parliament; IRV is used in some mayoral elections and local elections in parts of the UK.

In short, IRV lets voters rank candidates and ensures the winner has broad support by transferring votes from less-popular candidates to the remaining ones until someone reaches a majority. It’s one of several ranked-choice voting methods used around the world.