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#votingsystems#instant-runoffvoting#favoritebetrayal

How our voting system (and IRV) betrays your favourite candidate

The Center for Election Science

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  • Recommended by 5 people: 5 on Hacker News.
  • A classic. People kept recommending it from 2014 to 2021.
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Beginner. No background in the topic needed.

34K views12 years ago5 recommendations

Computer scienceComputation and complexityMath for programmers

An explanation of the favorite betrayal criterion and why instant-runoff voting can sometimes cause your least favorite candidate to win.

Most people know that you can't always vote for your favorite candidate in plurality voting. Your favorite might be a spoiler and your vote might cause your least favorite candidate to win. No matter how much you like him, you may have to betray your favorite candidate and vote for a candidate that actually has a chance of winning. Does Instant Runoff Voting (aka Ranked Choice Voting) fix this problem? No! This video clearly shows why sometimes, even in instant runoff voting, supporting your favorite candidate can cause your least favorite to win. You may need to betray your favorite and put for your first choice the candidate that has a better chance of beating your least favorite. Nader image by Don LaVange (cropped) (CC-BY 2.0): flickr.com/photos/wickenden/474602694/

Why it's here

5 people recommend this

What people say. Recommended for its clear, visual explanation of the flaws of instant-runoff voting and the favorite betrayal anomaly.

ClayShentrupon Hacker News • Recommends

On “Police Use Department Wish List When Deciding Which Assets to Seize”

This issue has been solved by math PhD's and political scientists who've studied the matter for decades. www.electology.org/approval-voting-vs-irv IRV can elect X even if Y was preferred to X by an arbitrarily huge majority and got more first-place votes than X. www.electology.org/core-support Regarding favorite betrayal, you might enjoy this video. link to this video
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aninhumeron Hacker News • Recommends

On “Show HN: Mest – Place to talk with those you disagree with”

This is a shorter video from the same source as the other reply that deals specifically with IRV: link to this video >Unless I misunderstand IRV, there is no "vote stealing" due to your vote automatically dropping off to your next-preferred candidate. The problem is that they drop to your next preferred candidate who has not been eliminated . If you're thinking about the problems that occur with plurality voting, it's easy to imagine your second choice will always be a popular "safe" choice, but if third parties get stronger (which is surely the point?) those safe choices can end up being eliminated before your second choice can help them.
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user234683on Hacker News • Recommends

On “Ranked-choice voting is on the ballot in New York City”

I always recommend this pair of videos when discussing STAR voting vs other alternative systems. The first video is an easy-to-follow explanation of how spoiler effects can happen in both plurality voting and IRV 1. In the second 2, the guy who created Star voting applies Ka-Ping Yee's methods to Star voting and animates it side-by-side with alternative systems to show its performance. 1 link to this video 2 link
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godelskion Hacker News • Recommends

On “What is ranked-choice voting and why is New York using it?”

RCV doesn't solve what is claimed in the article. It is interesting since countries that they give as examples are clear evidence of this. (Yes, I'm going to advocate cardinal systems like Approval, Range/Score, and STAR) > More moderate candidates. RCV doesn't encourage this at all. Australia is a clear example of this. In the house Liberal and Labor (the two major parties) control 85% of seats. The next major party (National) is part of a coalition with the Liberals and this sums to 95%. Things are only slightly better in the senate. Look at any country that uses IRC/RCV and you'll see a similar pattern. The system didn't encourage more parties and more moderates, Australia still has divid…
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elihuon Hacker News • Recommends

On “What is ranked-choice voting and why is New York using it?”

I agree with what /u/zestyping says in the other comment, so I won't repeat it. But here's a video explaining the strategic voting issue: link to this video Also, wikipedia has an example of a non-monotonic result here: link
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aninhumeron Hacker News • Mentions

On “When Lobbying was Illegal”

Yes, I understand how IRV works, and indeed I used to believe it was flawless. >There is no way that placing your preferred candidate first can ever result in your vote not being given in the order you choose. No, but it can end up harming your second choice, by eliminating them early, so your vote for them doesn't matter. This is called Favourite Betrayal, and it's a serious problem with IRV: link to this video And as a quick worked example, if you have 4 people voting A>B>C, 4 people voting C>B>A and 3 people voting B>A>C, then A wins. If one person voting C>B>A changes their vote to B>C>A, then B wins. So by putting C first, they were harming their second choice B.
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anderskaseorgon Hacker News • Mentions

On “Voting Paradoxes [video]”

…by the Debian, Ubuntu, and Gentoo projects, among many other organizations. link The video asserts that what it presents as “elimination voting”, usually known as instant-runoff voting, doesn’t suffer from the third-party spoiler effect. But that’s only true as long as the third party never gains enough support to have a real chance of winning. link to this video (I wonder: can you think of a pair of powerful organizations who might want to ensure that third parties never gain enough support to have a real chance of winning? Hmmm.) Finally, the video doesn’t talk about approval voting or score voting, which use a different ballot type to which Arrow’s impossibility theorem does not apply. Some game…
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aninhumeron Hacker News • Mentions

On “How Does the Electoral College Work and Is It Fair”

The problem with Instant Runoff is called "Favourite Betrayal", where placing a party second can lead to them being eliminated before your vote for them can be counted. link to this video >a candidate can still be elected despite not being approved or preferred by a majority. Only if there are no candidates preferred by a majority, in which case no voting system can produce a result people are happy with. The only way a ranked system could avoid this is by forcing people to choose between options they hate, and calling that a majority, which doesn't seem much better than letting someone with 30% approval win because it was the most. In fact, there's no reason you couldn't add a majority victory criteri…
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ClayShentrupon Hacker News • Mentions

On “Maine Ranked Choice Voting Initiative Approved”

No, IRV does not eliminate the spoiler effect. link to this video Score Voting and Approval Voting are simpler and better. link link
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ClayShentrupon Hacker News • Mentions

On “Approval Voting versus Instant Runoff Voting”

…cience and have studied voting methods since 2006). The idea behind LNH is that if I vote for the Green in 1st place, it's "safe" to then rank the Democrat 2nd, because that can't cause the Democrat to defeat the Green. See this explained visually in this video by Andy Jennings, another CES co-founder who did his math PhD thesis on voting methods. link to this video The Later-no-harm criterion is highly misleading, because "safe" here means safe for the CANDIDATE. But tactical voting is about what's good for the VOTER, not the candidate. With IRV, the Green voter's best strategy is to actually rank the Democrat in 1st place. So the whole notion that he can safely rank the Democrat #2 after he's ranked…
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ClayShentrupon Hacker News • Mentions

On “Ross Perot Has Died”

> with ranked choice voting the stigma of voting third party is removed That is a myth. Instant Runoff Voting does not eliminate the lesser evil (spoiler) problem. See this explained by a math PhD. link to this video
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ClayShentrupon Hacker News • Mentions

On “Ross Perot Has Died”

This is false. See the game theory explained by Andy Jennings, who did his math PhD thesis on voting methods and co-founded the Center for Election Science. link to this video Here's a more technical explanation by Warren Smith, a Princeton math PhD whose work was the centerpiece of the book "Gaming the Vote". link Finally, see real world data from a century of IRV in Australia. link
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ajenningson Hacker News • Mentions

On “Ranked-choice voting is on the ballot in New York City”

If Nader takes enough votes from Gore, then Gore will have the fewest first place votes and get eliminated first. Then Nader has to go up against Bush and it all comes down to who the Gore voters put as their second choice. It may only take a small percentage of them putting Bush second for Bush to win. link to this video Was this election spoiled? By Nader or by Gore? You can argue the semantics of what "spoiler" means, but to me it's clear that IRV doesn't handle this situation well. It is safe to vote for a third-party only if they can't win. When three-way elections get close, you have to be more careful.
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ClayShentrupon Hacker News • Mentions

On “Oppose the Earn IT Act”

…r prefers X to Y. That causes big problems. link It is precisely why ranked voting methods like Instant Runoff Voting are so vulnerable to tactics. If I prefer the Green, my general best strategy is to tactically rank the Democrat in 1st place, thus "burying" the Green and making the mere appearance of un-electability a self-fulfilling prophecy. link to this video link The major moral of voting theory is to AVOID RANKED VOTING METHODS, favoring RATED voting methods like score voting, STAR voting, and approval voting. Here's a presentation I gave in 2015 to the Colorado League of Women Voters explaining more.…
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godelskion Hacker News • Mentions

On “Ranked-choice voting will be used in Maine’s presidential election, court rules”

…er. Even Arrow himself said that cardinal voting (Approval, score, STAR) is probably the likely answer. They also tend to be much simpler as they only are single rounds and resistant to people accidentally "ranking" two candidates equally (which you might actually favor two candidates equally and these methods let you express that). 0 link 1 link to this video 2 link 3 link 4 link 5 link…
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ruytlmon Hacker News • Mentions

On “Ranked-choice voting will be used in Maine’s presidential election, court rules”

Perhaps I am suffering a failure of imagination, but in what circumstance does "ranking someone too high .. cause them to lose"? Edit: Found this0 talking about it; what remains unclear to me is whether this should be seen as "this hurts my candidate" over "this result better reflects the electorate". 0: link to this video
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