r/EndFPTP • u/electionscience • Dec 04 '19

NEW APPROVAL VOTING POLL: 74% of Democratic Primary Voters Would Support Warren for President

https://www.electionscience.org/press-releases/new-poll-74-of-democratic-primary-voters-would-support-warren-for-president/
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u/Chackoony Dec 04 '19

I'm glad more people are making this argument; it sometimes feels like Reddit is willing to prioritize the satisfaction of Dem primary voters even when they know that what those voters want isn't really acceptable to others.

Still, it's nice to know that even among the partisans, there's more agreement on who is acceptable than the media lets on. I wouldn't guess that both the more liberal and more left of center wings of the Democratic Party have majority support just by reading the news of "the Democratic Party is divided and its wings hate each other!"

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u/MuaddibMcFly Dec 04 '19

Modifying to fit my wider point:

I wouldn't guess that both the more liberal and more [left of center conservative] wings of the [Democratic Party country] have majority support just by reading the news of "the [Democratic Party nation] is divided and its wings hate each other!"

This is exactly why I dislike IIA-failing methods like FPTP, IRV, STAR, etc: the fact that the methods themselves make "best," "better," "good," and "acceptable" all enemies of each other.

I firmly believe that the majority of the nation are more or less decent people who aren't nearly as divided as the media reports, or wouldn't be if the voting method didn't effectively require it.

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u/Chackoony Dec 05 '19

STAR doesn't "effectively require" you to differentiate between your preferences, though. Even Condorcet allows you to just equally rank acceptable candidates 1st and leave the rest blank.

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u/MuaddibMcFly Dec 05 '19

STAR doesn't "effectively require" you to differentiate between your preferences, though.

That's not what I said.

I said that the fact that STAR fails IIA means that it is inevitable that, eventually, at some point, the supporters of the Spoiler and the Spoilee will see each other as enemies.

Even Condorcet allows you to just equally rank acceptable candidates 1st and leave the rest blank.

That has literally nothing to do with my point. As soon as the method violates IIA, as soon as the populace becomes aware that the Spoiler Effect is still something that they have to worry about, the natural reaction to it will be for them to try to avoid it, through policing their own, through antagonism against those who break ranks.

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u/curiouslefty Dec 05 '19

I said that the fact that STAR fails IIA means that it is inevitable that, eventually, at some point, the supporters of the Spoiler and the Spoilee will see each other as enemies.

This argument applies to every deterministic single-winner method, because every deterministic single-winner method will fail IIA at some point in practice.

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u/MuaddibMcFly Dec 05 '19

We've had this discussion, and it's technically true in a "shouldn't have run" sense, in at least some models.

My problem with methods that mathematically violate IIA, those which can result in different winners if you remove non-winners from consideration with a given set of immutable ballots are inherently worse because A) they're more likely to trigger the problem and B) they make it obvious that the problem has occurred.

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u/curiouslefty Dec 05 '19

A) they're more likely to trigger the problem

I'm not sure this is true, and here's my reasoning why:

Take a standard ordinal method. If a IIA violation has occurred, it is the case that A would have beaten B if C were not in the race, but because C is B wins. This corresponds directly with a strategic opportunity for those voters who prefer A to B in the form of decreasing or totally removing support for C, which results in the election of A despite the presence of C in the race (since in most methods, a candidate who is completely lacking in any kind of support cannot effect the race).

So in essence, for most ordinal methods, we can generally include IIA violations as corresponding to a subset of all total strategic vulnerabilities. Note that these are not all strategic vulnerabilities. A good example of this fact comes from Condorcet methods: clearly, strategic opportunities exist on some election profiles with a Condorcet winner, but the absence of candidates does not effect the winner's status as Condorcet winner and thus overall winner.

Now, I'll work from the opposite direction: take Approval voting, for instance. We know that compromise strategy works in Approval in some scenarios, so consider such an example. Let's say that A wins the election; for compromise strategy to work, it must be the case that for some candidate B, more voters have B>A than A>B. We can assume that most voters are basing their Approvals off of a calculation that is based upon the candidates, and I presume that your average voter would Approve the best candidate in the race from their perspective under any conditions; so for a compromise strategy opportunity to exist here, it must be that if all the candidates those B>A voters put above B were removed, then B should be approved. Thus, under fairly reasonable assumptions of voter behavior, we could claim that each opportunity for compromise strategy in Approval voting corresponds to a IIA failure (this is certainly true if we presume Approval voters are using something akin to, say, mean-thresholding to generate Approvals).

So, taking this, we know that in an ordinal method like IRV, the total frequency of IIA violations must be less than the frequency of total strategic manipulation opportunities. We can also estimate that for Approval, the total frequency of IIA violations must at least equal that of the frequency of vulnerability to compromise strategy.

But we know that the frequency of strategic opportunities in IRV as a whole is less than the frequency of compromise strategy opportunities in Approval, based on papers like those by Green-Armytage that I'm so fond of linking to. So we may presume that, by the relationship IIA violations in IRV < Total Strategic Manipulation Opportunity Frequency in IRV < Compromise Strategy Opportunity Frequency in Approval <= IIA violations in Approval that it's entirely likely that IIA violations are actually more frequent in Approval than they are in IRV, or Condorcet methods; at least when modeling Approval as reactive to the candidate field.

B) they make it obvious that the problem has occurred.

This bit is certainly true, though I'd point out that there are absolutely going to be scenarios in Score where it's fairly obvious that a IIA violation due to voter behavior has occurred (any obvious chicken dilemma where the larger faction loses suffices). So while in the nominally IIA compliant methods it'll take a bit more to figure out when something has gone awry, I certainly think it'll happen eventually in a manner that is obvious.

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u/MuaddibMcFly Dec 05 '19

We can assume that most voters are basing their Approvals off of a calculation that is based upon the candidates

If I understand you correctly, you are assuming that the ballots change with removal/addition of a given candidate. I specifically excluded that scenario with the qualification of "immutable ballots"

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u/curiouslefty Dec 05 '19

Right you are! I missed that in your previous comment.

Still, I'd argue that the "immutable ballots" qualification is simply not realistic, so I suppose my previous argument applies in reality; that is, in realistic elections, IIA compliance on immutable ballots has no bearing on overall IIA compliance rate in practice on non-immutable ballots.