Instant-Runoff Voting (IRV)
Instant-runoff voting (IRV) lets voters rank candidates. The candidate with the fewest first-choice votes is eliminated, and ballots transfer to the next remaining preference. Rounds continue until a candidate has a majority of the continuing votes. The system can reduce vote splitting, but does not eliminate every spoiler scenario.
THE IDEA
USING THE WHOLE COW, IN AUSTRALIA AND VERMONT
Let me tell you how they do it in Australia.
The ballot down under looks a lot like Borda's. You don't just mark your ballot with the candidate you like best; you rank all the candidates, from your favorite to the one you hate the most.
A simplified scenario based on Florida 2000 illustrates how the Australian system counts those preferences.
Start by counting the first-place votes, and eliminate the candidate who got the fewest. In this case, that's Nader. Toss him! Now we're down to Bush vs. Gore.
But just because we threw Nader out doesn't mean we have to throw out the ballots of the people who voted for him. (Use the whole cow!) The next step—the "instant runoff"—is the really ingenious one. Cross Nader's name off every ballot and count the votes again, as if Nader had never existed. Now Gore has 51% of the first-place votes: the 49% he had from the first round, plus the votes that used to go to Nader. Bush still has the 49% he started with. He has fewer first-place votes, so he's eliminated. And Gore is the victor.
What about our slightly modified version of Florida 2000, where we moved 2% from "Gore, Nader, Bush" to "Bush, Gore, Nader"? In that situation, Gore still won the Borda count. By Aussie rules, it's a different story. Nader still gets knocked off in the first round; but now, since 51% of the ballots place Bush higher than Gore, Bush takes the prize.
The appeal of instant-runoff voting (or "preferential voting," as they call it in Australia) is obvious. People who like Ralph Nader can vote for him without worrying that they're throwing the race to the person they like least. For that matter, Ralph Nader can run without worrying about throwing the race to the person he likes least.[*]
Instant-runoff voting (IRV) has been around for more than 150 years. They use it not only in Australia but in Ireland and Papua New Guinea. When John Stuart Mill, who always had a soft spot for math, heard about the idea, he said it was " among the very greatest improvements yet made in the theory and practice of government."[*]
When to use it
Electing a single winner from a field of multiple candidates in political elections.
Preferential voting for organizational leadership positions.
Avoiding wasted votes in multi-candidate races.
Comparing ranked voting rules when choosing an election procedure.
FROM THEORY TO EVERYDAY LIFE
In practice
A simplified Florida 2000 scenario
In Ellenberg’s simplified scenario based on Florida 2000, Nader has the fewest first-choice votes and is eliminated. The assumed rankings transfer his supporters’ votes to Gore, giving Gore 51% and Bush 49%. This illustrates the counting rule; it is not an observed result under IRV.
Modified Florida 2000 with swapped preferences
In a modified scenario where 2% of voters changed their preference from 'Gore, Nader, Bush' to 'Bush, Gore, Nader', Nader is still eliminated first. However, now 51% of ballots place Bush higher than Gore, so Bush wins, unlike under Borda count where Gore still wins.
A MOMENT TO REFLECT
Put it to work.
How does instant-runoff voting help solve the spoiler effect seen in plurality voting?
In what scenarios might IRV fail to produce a majority winner?
Why is it called "use the whole cow"? What does that metaphor imply about preference information?
Often confused with
CONTINUE THE CONVERSATION
Source texts
- How Not to Be Wrong The Power of Mathematical Thinking (Ellenberg, Jordan)