Instant runoff voting (IRV)
Also called ranked-choice voting (RCV) in the U.S., the alternative vote (AV) in the U.K., and preferential voting in Australia.
Instant runoff voting (IRV) is a way of counting ranked ballots. If no option is the first choice of more than half the voters, the option with the fewest first choices is knocked out, and those ballots move to their next choice. That repeats until one option has a majority of the ballots still in play.
- Nickname
- The elimination game
- Single-winner form
- Proposed in the 1870s
- Used for
- Australia's House of Representatives, Ireland's president, Maine's elections, New York City's primaries, the Oscar for Best Picture
- Best at
- Making sure the winner has a majority in the final round
- Watch out for
- A broadly liked option getting knocked out early
How it works
- Count first choices. Each ballot counts as one vote for its top-ranked option.
- Check for a majority. If one option has more than half of the votes, it wins.
- Knock out last place. Otherwise, the option with the fewest votes is eliminated.
- Move those ballots. Each ballot for the eliminated option now counts for its next choice that's still in the race. Then go back to step 2.
It's called instant because it works like a series of runoff elections without anyone returning to vote: the ballots already say who each voter would pick next.
| 🌮 Tacos | 🍣 Sushi | 🍕 Pizza | |
|---|---|---|---|
| Round 1 | 4 | 3 | 2, out |
| Round 2 | 4 | 5, wins |
Pizza has the fewest first choices, so it's out, and its two ballots move to their second choice, sushi. Sushi wins, five to four. Notice that pizza was every friend's first or second choice, yet it went out first. See this count acted out in the story.
A short history
- 1788
The French mathematician the Marquis de Condorcet describes eliminating the last-place option round by round, but only to criticize it. He preferred head-to-head comparisons, now called the Condorcet method.
- 1850s
Carl Andræ in Denmark and Thomas Hare in England each design the single transferable vote, a way to elect several people at once by transferring votes between candidates.
- 1870s
The American architect William Robert Ware proposes using the same idea to elect a single winner. That's instant runoff.
- 1918
Australia uses it for a federal election for the first time, in the Corangamite by-election. The Labor candidate leads the first count with 42.5%, but after preferences move, a farmers' candidate wins with 56.3%. Australia has elected its House of Representatives this way ever since.
- 1937
Ireland's new constitution has its president elected with transferable votes, which for a single winner is instant runoff. In 1990, Mary Robinson trails Brian Lenihan in the first count, 38.7% to 43.8%, then wins with 51.6% after the third-place candidate's ballots move.
- 2009
The Academy of Motion Picture Arts and Sciences starts choosing the Oscar for Best Picture with a preferential ballot.
- 2011
The United Kingdom holds a referendum on switching to the “alternative vote” (AV), its British name, for Parliament. About two-thirds vote no.
- 2016
Maine becomes the first U.S. state to adopt it statewide, by a ballot measure. It's first used in 2018.
- 2020s
New York City uses it for primaries starting in 2021, and Alaska for its elections starting in 2022. A 2024 measure to repeal it in Alaska fails by fewer than a thousand votes, while several other states pass laws banning it.
Strengths and weaknesses
Strengths
- A majority in the final round. The winner always has more than half of the ballots still counting at the end.
- Similar options don't spoil each other. If two candidates appeal to the same voters, whichever one is knocked out passes its ballots to the other, instead of splitting the vote like a show of hands does.
- Your backup choices can't hurt your favorite. Lower rankings only count after your favorite is knocked out, so ranking a second choice never helps it beat your first. That makes it safe to rank honestly.
- Easy to explain. “Knock out last place and recount” is familiar from runoff elections, and it saves the cost and low turnout of a second election day.
Weaknesses
- The center can get squeezed. An option that's almost everyone's second choice may have too few first choices to survive the early rounds, even if it would beat every other option one-on-one.
- More support can backfire. In rare cases, ranking an option higher can make it lose, by changing which option is knocked out first. That's called a monotonicity failure.
- It has to be counted in one place. Each round depends on the last, so results can't simply be added up precinct by precinct. Counting can take days.
- Some ballots stop counting. If every option you ranked is knocked out, your ballot is “exhausted,” so the final majority is of the ballots still in play, not of everyone who voted.
How it does on the fairness tests
- Passes: if more than half the voters rank an option first, it wins.
- Passes: ranking a backup can't hurt your favorite.
- Passes: similar options don't split the vote.
- Fails: an option that beats every other one-on-one can still lose.
- Fails: more support can, rarely, make an option lose.
- Fails: results can't be counted in separate places and added up.
Questions
- Is instant runoff (IRV) the same as ranked-choice voting (RCV)?
- In the U.S., yes: “ranked-choice voting,” or RCV, almost always means IRV. Strictly speaking, ranked choice describes the ballot, and instant runoff is one of several ways to count it.
- Does my vote count if my first choice is knocked out?
- Yes. Your ballot moves to your next choice that's still in the race, as long as you ranked one.
- Should I rank every option?
- If you have a preference between them, ranking more options means your ballot keeps counting in later rounds. Ranking a backup never hurts your favorite.
- How is it different from a regular runoff election?
- A regular runoff holds a second election between the top two, weeks later. Instant runoff does it all from one ballot, and it can knock options out one at a time instead of all but two at once.