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> If it's a close three-way election, you might cause your favorite candidate to lose by ranking them first. Could you explain that? I can't think of a situati

> If it's a close three-way election, you might cause your favorite candidate to lose by ranking them first. Could you explain that? I can't think of a situation where putting the candidate I want to win as #1 would cause them to lose. Ranking other close candidates as #2/#3 could cause my #1 to lose, but I don't think voting for someone as #1 alone would possibly harm them.

godelski 4y ago
So what I think the parent is referring to is called the Favorite Betrayer Criteria[0]. The short is that there are two forms of the spoiler effect: strong and weak. RCV handles the weak case but does not handle the strong case. I explain part of why cardinal methods handle the strong case in this comment[1]. The truth is that we're far more concerned with the strong case than weak case because from our current position this is the more frequent type of spoiler (and arguably is more frequent in general). [0] https://electowiki.org/wiki/Favorite_betrayal_criterion https://electowiki.org/wiki/Favorite_betrayal_criterion [1] https://news.ycombinator.com/item?id=33111242 https://news.ycombinator.com/item?id=33111242
- bombcar 4y ago
  I wonder if fixing the "strong case" spoiler actually is NOT what some "spoiler voters" would want, simply BECAUSE they want to spoil for the other party to try to move that party toward where they want it to be.
  - godelski 4y ago
    Probably. But I don't think the public really wants their voting systems to be highly vulnerable to strategic voting. That does just give elites an edge and ends up with less equitable representation. (strategies exist for ALL voting systems. But not all strategies are equally as bad)
    - dane-pgp 4y ago
      > not all strategies are equally as bad That's an important point. Also, just because a strategy exists in theory, doesn't mean that in practice any voter can confidently find that strategy (since they lack perfect information about how all the other voters intend to vote).
    - naniwaduni 4y ago
      Also, not all "strategies" fit people's intuitive notion of "strategy", which is colored by FPTP having a really glaringly awful strategic incentive for dishonest voting.
      - godelski 4y ago
        Most cardinal systems make it difficult to vote strategically. That's actually what the difference with star and score is about. But this is also why so many in the thread are talking about monotonicity and favorite betrayer. Failing these criteria means your voting system is highly susceptible to manipulation. Essentially allowing candidates to win that shouldn't have won.
achr2 4y ago
Let's say you have three candidates A, B, C. A is left, B is center, C is right leaning. Polling shows that voters are leaning: - 15% BAC - 15% BCA - 25% ABC - 45% CBA If everyone voted as they desired, then the instant runoff would be between B and C, with B winning with 55% of votes. If a subset of C voters instead strategically vote ACB (6%), this would change the runoff to be between A & C, with C winning 60%.
- bena 4y ago
  First, a run off between A and C wouldn't have C with 60%. C would have 54%, the 6% of C voters would have to come from CBA. And if A is in the runoff, that 6% stays with A. These are post facto strategies though. You can only implement that strategy if you can guarantee all of that information. Which you can only do after the election. The first problem is that polling is an estimate. If you are wrong by a couple of percentage points, the strategy fails. If the results come back 16 (BAC), 16 (BCA), 23 (ABC), 39 (CBA), 6 (ACB), B now has 32 first votes and A only has 29. Next is getting the right number of people to comply. You could easily just mess it up and have either not enough or too many people cast the strategic ballot. If only 4% or less vote ACB, the plan doesn't work. If 11% or more vote ACB, A wins. In the end, strategic voting is a bit like voter fraud, talked about way more than is actually done. And implied to be a much bigger problem than it ever could be.
  - achr2 4y ago
    Oh I don't disagree, and am in the strong support of anything that moves away from FPP. The only addition I will make is that these (potentially unfounded) fears is what leads people to continue to vote strategically, such as voting BAC instead of ABC to avoid the potential of C using the strategy.
- crazygringo 4y ago
  And just to be clear, this makes sense. Because the relevant fact here isn't that some CBA voters put A at the front (ACB). It's that they moved B from 2nd to 3rd. So of course, that lessens support for B, so B no longer wins. People seem to present this as a flaw, when it's reflecting actual changes in voting. And this is basically impossible to do so strategically, because nobody has this level of accurate detail prior to the election.

godelski 4y ago

So what I think the parent is referring to is called the Favorite Betrayer Criteria[0]. The short is that there are two forms of the spoiler effect: strong and weak. RCV handles the weak case but does not handle the strong case. I explain part of why cardinal methods handle the strong case in this comment[1]. The truth is that we're far more concerned with the strong case than weak case because from our current position this is the more frequent type of spoiler (and arguably is more frequent in general). [0] https://electowiki.org/wiki/Favorite_betrayal_criterion https://electowiki.org/wiki/Favorite_betrayal_criterion [1] https://news.ycombinator.com/item?id=33111242 https://news.ycombinator.com/item?id=33111242

bombcar 4y ago
I wonder if fixing the "strong case" spoiler actually is NOT what some "spoiler voters" would want, simply BECAUSE they want to spoil for the other party to try to move that party toward where they want it to be.
- godelski 4y ago
  Probably. But I don't think the public really wants their voting systems to be highly vulnerable to strategic voting. That does just give elites an edge and ends up with less equitable representation. (strategies exist for ALL voting systems. But not all strategies are equally as bad)
  - dane-pgp 4y ago
    > not all strategies are equally as bad That's an important point. Also, just because a strategy exists in theory, doesn't mean that in practice any voter can confidently find that strategy (since they lack perfect information about how all the other voters intend to vote).
  - naniwaduni 4y ago
    Also, not all "strategies" fit people's intuitive notion of "strategy", which is colored by FPTP having a really glaringly awful strategic incentive for dishonest voting.
    - godelski 4y ago
      Most cardinal systems make it difficult to vote strategically. That's actually what the difference with star and score is about. But this is also why so many in the thread are talking about monotonicity and favorite betrayer. Failing these criteria means your voting system is highly susceptible to manipulation. Essentially allowing candidates to win that shouldn't have won.

achr2 4y ago

Let's say you have three candidates A, B, C. A is left, B is center, C is right leaning. Polling shows that voters are leaning: - 15% BAC - 15% BCA - 25% ABC - 45% CBA If everyone voted as they desired, then the instant runoff would be between B and C, with B winning with 55% of votes. If a subset of C voters instead strategically vote ACB (6%), this would change the runoff to be between A & C, with C winning 60%.

bena 4y ago
First, a run off between A and C wouldn't have C with 60%. C would have 54%, the 6% of C voters would have to come from CBA. And if A is in the runoff, that 6% stays with A. These are post facto strategies though. You can only implement that strategy if you can guarantee all of that information. Which you can only do after the election. The first problem is that polling is an estimate. If you are wrong by a couple of percentage points, the strategy fails. If the results come back 16 (BAC), 16 (BCA), 23 (ABC), 39 (CBA), 6 (ACB), B now has 32 first votes and A only has 29. Next is getting the right number of people to comply. You could easily just mess it up and have either not enough or too many people cast the strategic ballot. If only 4% or less vote ACB, the plan doesn't work. If 11% or more vote ACB, A wins. In the end, strategic voting is a bit like voter fraud, talked about way more than is actually done. And implied to be a much bigger problem than it ever could be.
- achr2 4y ago
  Oh I don't disagree, and am in the strong support of anything that moves away from FPP. The only addition I will make is that these (potentially unfounded) fears is what leads people to continue to vote strategically, such as voting BAC instead of ABC to avoid the potential of C using the strategy.
crazygringo 4y ago
And just to be clear, this makes sense. Because the relevant fact here isn't that some CBA voters put A at the front (ACB). It's that they moved B from 2nd to 3rd. So of course, that lessens support for B, so B no longer wins. People seem to present this as a flaw, when it's reflecting actual changes in voting. And this is basically impossible to do so strategically, because nobody has this level of accurate detail prior to the election.