[EM] Ultimate SPE Agenda Processing: Sink Swap Bubble

[Forest Simmons]

On Mon, Apr 3, 2023, 2:20 AM Kristofer Munsterhjelm <km_elmet at t-online.de>
wrote:

> On 4/1/23 18:27, Kevin Venzke wrote:
> > Hi Forest,
> >
> > Le samedi 1 avril 2023 à 10:31:08 UTC−5, Forest Simmons <
> forest.simmons21 at gmail.com> a écrit :
> >> Here's an example of another standard test case for Sink Swap Bubble
> ("Bubba" for short).
> >>
> >> 48 C
> >> 28 A>B
> >> 24 B (sincere is B>A)
> >>
> >> The smallest faction has thrown the sincere CW under the bus ...
> knowing that most Condorcet
> >> methods, including classical wv methods like Ranked Pairs, would break
> the resulting ABCA
> >> beat cycle at the weakest defeat A>B, leaving B as the winner.
> >
> >> Bubble changes the order to B<A<C ... the finish order of the method
> ... thus disappointing
> >> the defecting faction with a finish order polar opposite to their
> sincere preferences ...
> >>
> >> When will they learn that you cannot mess with Bubba?
> >
> > I've said this before, but I'm not a fan of this kind of method because,
> what if you're
> > wrong about the sincere preferences? Then by electing C, you're actually
> punishing the A>B
> > voters for not using compromise strategy. This muddies the water as to
> what behavior
> > "chicken resistance" is actually incentivizing.
>
> This is about chicken resistance in general, no? I suspect there's a
> more general impossibility result hiding here: that methods that are
> burial resistant and Condorcet (in the way the Smith-IRV hybrids or
> Friendly is) have to make uncharitable interpretations of ballots that,
> if they were honest, would imply a very different candidate should be
> elected. (I have no proof of this, but it seems a reasonable hunch.)
>

This is exactly what I have found. Classical Condorcet assumes honest,
sincere voters with imperfect estimation of the truth ... wv majorities
have the best chance of discerning that truth. But, as examples show ...
these methods are easily subverted by unscrupulous opportunistic
sophisticated voyers.... and as you and Kevin have noted, methods that
punish burial and defection must sacrifice VSE ... until the unscrupulous
learn it will almost always back fire.  When everybody learns that lesson,
the sincere CW will be a ballot CW much more frequently.

>
> It's kind of like the "weak centrist! Condorcet winner! weak centrist!
> Condorcet winner!" thing cardinal proponents mention.
>
> So if I'm right, then either we can choose a method that produces a very
> good result with honesty, or one that deters burial strategy, but not
> both.


Well put!

And then the ultimate deluxe method (in one sense) would be
> something along the lines of:
>
> - Conduct an election with "honest" method X and "suspicious method" Y
> (or putting it differently, "compromise resistant" X and "burial
> resistant" Y).
> - If the winners are equal, we're done.
> - Otherwise do a manual runoff, where the voters' behavior will be
> honest (majority rule with two candidates is incentive compatible).
> Elect the winner.
>

That's easier said than done ... definitely needs more explorstion.

It turns out that Agenda chain Climbing is of the highly burial resistant
type, while Agenda Uncovering is better for honesty ... remember it says ...
Elect the most favorable agenda alternative unless it is covered ... in
which case elect the most favorable alternative that covers it ... unless
it too is covered.... in which case elect the most favorable alternative
that covers it ...etc. ... An ideal Landau method for honest voters.

But hears the subtle difficulty of a combo method:

Suppose C is the sincere CW and A creates a cycle by burial of C under the
bus B. The honest methods, including wv, SPE, Agenda Uncovering, etc. ...
all choose A. The burial resistant methods all choose the bus B.

A sincere runoff between A and B will choose A.

On the other hand, the sincerity checks of Bubba and Agenda Chain Climbing
will restore C.

But restoring C makes burial less risky for the buriers!

It's like parents trying to figure out how to discipline their children
without negative consequences. Alfie Kohn wrote the book on that topic ...
"Punished by Rewards" ...

>From another POV it's the uncertainty principle in action!


> But that might be asking for *too* much in the complexity department.
>
> If you were to agree with the cardinal proponents, then X could even be
> something like Smith|Range (| being normalization) or STAR. But I tend
> to agree with rb-j that cardinal ballots are undefined. Even von
> Neumann-Morgenstern utility elicitation can be really difficult -- I've
> tried it a few times.
>
> -km
>
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