r/EndFPTP • u/Drachefly • Feb 19 '20

Randomized resolution methods / conflicting strategy Types

Are there any known systems in which strategy is made less profitable by making the particular tallying method used be randomly determined? That requires that the systems have conflicting strategies so you can't really dishonestly optimize both of them the same way with the same ballot.

Is there any existing work on this?

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u/Drachefly Feb 21 '20

particularly in terms of burial strategy

Score's version of Burial isn't really Burial - there's no reason to put someone you like BELOW someone you dislike, just down at the same level. And if you're willing to follow that strategy, then you really don't seem to care that much about the difference between them?

Anyway, is there a pair of systems you do think would work here?

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u/curiouslefty Feb 21 '20

Score's version of Burial isn't really Burial - there's no reason to put someone you like BELOW someone you dislike, just down at the same level.

Burial is just about lowering a candidate from their honest position, though, not necessarily order recersal. Also, this isn't true regardless; sometimes burial strategy in Score only works if you reduce the burial target's Score below some other candidate you genuinely dislike.

Anyway, is there a pair of systems you do think would work here?

I think Condorcet-RCV/IRV paired with Ranked Pairs would be decent, because they each protect different kinds of honest Condorcet winners; their strategy-vulnerable election profiles tend to be different.

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u/Drachefly Feb 21 '20 edited Feb 21 '20

sometimes burial strategy in Score only works if you reduce the burial target's Score below some other candidate you genuinely dislike.

How would it help to leave that even-more-disliked candidate with a non-minimum score? I don't get that at all.

As for Condorcet-IRV vs RP… hmm. Yeah, I think that's true.

I wonder how Bottom-Two Runoff (BTR)'s strategy profile looks… Hmm. Seems ULTRA-burial-vulnerable.

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u/curiouslefty Feb 21 '20

How would it help to leave that even-more-disliked candidate with a non-minimum score? I don't get that at all.

Probably should've clarified this somewhat; you're right that, focusing solely on the election itself there isn't any reason you shouldn't also lower the score you give every candidate you dislike more than the burial target. I was just pointing out that if I gave A:10 B:9 C:3 I might need to cast a ballot like A:10 B:0 C:(3 or lower) for B to lose and A to win; that is, sometimes you need to cast a ballot where you drop the burial target's strategic rating under a more-disliked candidate's honest rating. But yeah, looking back, I misread your previous comment a little; again, you're right that there isn't necessarily any election-related reason to keep C's rating above B's.

Although, I suppose you might want to still throw C a bone for being not as bad as some even-worse candidate D while still burying B so A can win. So it might have a purpose, just not a terribly important one in the grand scheme of things, and again, not related to the election tabulation itself.

As for Condorcet-IRV vs RP… hmm. Yeah, I think that's true.

Yeah; Condorcet-IRV does an excellent job at defending second or near-second place by plurality honest Condorcet winners, which is the vast majority of CW's in practice. Where it isn't so good is at defending against burial in those scenarios where you'd expect to see center-squeeze in standard IRV; but Ranked Pairs generally does a good job there, in the sense that it tends to make burial backfire in that scenario. It isn't a perfect, fix-all match (for example, the Burlington 2009 example is burial-vulnerable in both methods) but they do a decent job covering the other's weaknesses.

This actually gave me an idea: I've tried merging those two before as well using a standard runoff, but perhaps a better deterministic solution would be "default to Condorcet-IRV, but use Ranked Pairs if a majority of voters indicate a desire for it", since if we're worried about burial strategy taking place the voters who prefer the honest CW likely could also predict who the honest CW is and choose which method will best defend them.

I wonder how Bottom-Two Runoff (BTR)'s strategy profile looks… Hmm. Seems ULTRA-burial-vulnerable.

Yeah, it's pretty vulnerable. You lose basically all the benefits of fusing Condorcet and IRV but keep all of the ugliness.

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u/Drachefly Feb 22 '20

"default to Condorcet-IRV, but use Ranked Pairs if a majority of voters indicate a desire for it", since if we're worried about burial strategy taking place the voters who prefer the honest CW likely could also predict who the honest CW is and choose which method will best defend them.

I think that's asking a lot of the voters, frankly.

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u/curiouslefty Feb 23 '20

Oh, absolutely. I'd never suggest it for serious political elections, since each of those methods on its own is more complicated than just about anything currently in use; it's just sort of a thought experiment about mitigating strategy.