[EM] Strategy-free criterion

[Closed Limelike Curves]

>
> Something I will have to post about at some point is what a game-changer
> it is if we
> take it as an assumption that elections will have two frontrunners and all
> voters
> use frontrunner truncation strategy. Arbitrary-looking majority rules
> prove very
> useful in maximizing performance.
>
I think there's a big issue with assuming two frontrunners because A) in
that case, it's just a majority vote between them and B) you can have
situations where multiple candidates have strongly correlated scores, e.g.
if they're all from the same party.

This is why I previously suggested that, ideally, a system should satisfy
both zero-info honesty and LNHe+FBC. This seems like the maximally-honest
combination of properties, because it handles low-information elections
honestly, and high-information elections "as sincerely as possible" (i.e.
no order-reversal, which is enough to guarantee the Condorcet winner is
visible from the ballots).

STAR works off of a very similar principle. The hope is the first stage
will find two similar frontrunners, and then the second stage is
strategyproof (since it's a majority vote). This combination fails both
criteria in theory, but might satisfy them in practice. That's especially
true if you combine it with other improvements: countbacks, a master lever
for straight-ticket voting, and skipping the runoff if the top-two
finishers are from different parties could maximize the chances of STAR
working as it should.

I think the best hope for a system that formally satisfies both criteria is
probably somewhere in the generalized median family of voting methods.

On Sat, Jun 8, 2024 at 3:44 PM Kevin Venzke <stepjak at yahoo.fr> wrote:

> Hi Chris,
>
> > > MD basically says that if there are two frontrunners and everyone
> truncates their
> > > less liked frontrunner, then the worse frontrunner won't win. If this
> property
> > > doesn't hold, it means the majority has done something to stop the
> method from
> > > "seeing" their majority, which is surely that they ranked other
> candidates above
> > > the preferred frontrunner.
> >
> > Instead of "above the preferred frontrunner" don't you mean *below the
> > less-liked frontrunner*?
>
> I don't mean that, and I am not sure how "below the less-liked
> frontrunner" would
> apply? Who in 49/24/27 ranks a candidate below the less-liked frontrunner?
>
> > The classic example used by people who like Winning Votes and Approval
> > to flout those method's compliance with MD (versus the MD failures of
> > Margins and IRV):
> >
> > 49 A (sincere might be A>B)
> > 24 B  (sincere might be B>C)
> > 27 C>B (sincere)
> >
> > A>C  49-27 (=23)     C>B  27-24  (=3)    B>A  51-49  (=2)
> >
> > By Margins A's defeat is the weakest and MinMax (and methods that are
> > equivalent to it with only 3 candidates, such as Ranked Pairs and
> > Schulze) using margins elects A.
> >
> > But Minimal Defense says "not A" because more than half the voters voted
> > B above A and A not above equal-bottom.  MD has no problem with the 27
> > C>B voters who ranked a candidate above their preferred (presumably
> > perceived) "frontrunner."
>
> What I'm saying is that if a method fails MD in this scenario, the likely
> issue
> is that the C>B voters ranked C above B, and if they didn't do that, then A
> could've been defeated. In this scenario, that is fairly obvious, but it's
> true
> in general, that MD failures are almost always instances of a majority (or
> part of
> one) facing compromise incentive.
>
> In practice you can liken MD / SDSC to a weak form of the strong FBC, and
> liken SFC
> to a weak form of Later-no-harm.
>
> Incidentally I agree with what CLC seems to suggest, that you don't have
> to discuss
> burial to find merit in MD. There are methods with no burial incentive
> that satisfy
> MD and it is certainly not meaningless in those contexts, because it
> addresses
> compromise.
>
> > > I would not like to see SFC as totally obsolete, since it was one of
> the motivating
> > > criteria (along with MD and weak FBC) for my methods MDDA and MAMPO :)
> >
> > Inventing those methods was some achievement as a thought experiment to
> > demonstrate that certain criteria are mutually compatible.
> >
> > But MDDA spectacularly fails the maximum-absurdity criterion
> > Mono-add-Plump, a very interesting fact that isn't mentioned on its
> > electowiki page.
>
> I can hardly advocate MDDA now due to the Plurality failure. However, it
> performs
> very well in my truncation simulation, as does a method with very similar
> results,
> which I call RMPA (River Majority Pass Approval). However, RMPA doesn't
> actually
> satisfy FBC, so I can't list it in the same breath as the other two.
>
> In RMPA we go down the list of candidates in order of descending implicit
> approval,
> and process each candidate's full majority pairwise wins River-style
> (using the
> "bins" conception, I would suggest). There is no need to sort the
> propositions; it's
> enough to treat each candidate's wins in a batch with arbitrary order.
> Elect the
> owner of the "bin" that the approval winner ends up in.
>
> > Of course the method also fails Irrelevant Ballots Independence. If we
> now add 3
> > ballots that plump for X, the majority threshold rises to 52 and so C's
> > majority-strength defeat goes away and C wins again by being the most
> approved
> > candidate.
> >
> > This demonstration of Mono-add-Plump failure doesn't apply to MAMPO, but
> that method
> > would also fail Irrelevant Ballots Independence. It may be far less bad.
>
> Something I will have to post about at some point is what a game-changer
> it is if we
> take it as an assumption that elections will have two frontrunners and all
> voters
> use frontrunner truncation strategy. Arbitrary-looking majority rules
> prove very
> useful in maximizing performance.
>
> In such a setting I find that MAMPO is usually not as good as MDDA or
> RMPA, but all
> of them outperform all Condorcet methods at sincere Condorcet efficiency.
>
> It's a different approach from what I usually use, to say "let's just
> assume voters
> act in this way regardless of what the method is." We may not be standing
> on firm
> ground there. But I find it a bit intuitive to think voters will mainly
> truncate
> worse frontrunners. Compromise incentive isn't even completely ignored: By
> having
> voters refuse to compromise, methods that depend on it this to work well
> (such as
> FPP) are penalized in the analysis.
>
> Kevin
> votingmethods.net
>
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