[EM] DMTCBR and reversal symmetry

[Forest Simmons]

Btw, defeat strength (wfv-lfv) winning minus losing friendly votes/approval
is my current understanding of the natural destiny of the fpA-fpC odyssey.
Any additional thoughts on that?

-Forest

On Mon, Oct 24, 2022, 6:53 PM Forest Simmons <forest.simmons21 at gmail.com>
wrote:

> As I understand it, with RP, CSSD, and River, defensive truncation, eg
> below the putative CW will likely work as long as defeat strength is gauged
> with winning votes (wv), as opposed to margins.
>
> Any comments on that?
>
> And what if defeat strength is gauged by winning approval? ... especially
> winning friendly-approval (wfa)?
>
> -Forest
>
> On Mon, Oct 24, 2022, 5:54 PM Kevin Venzke <stepjak at yahoo.fr> wrote:
>
>> Hi Kristofer,
>>
>> Le lundi 24 octobre 2022 à 04:43:58 UTC−5, Kristofer Munsterhjelm <
>> km_elmet at t-online.de> a écrit :
>> > Thus a method that passes both DMTCBR and rev. sym. would be extremely
>> > resistant to both burial and to compromise. But since the favorite
>> > betrayal criterion is so hard to pass, we have reason to believe that
>> > this is impossible. So no such method can be rev. sym -- which is what
>> > we at least see with Condorcet methods!
>> >
>> > It's thus quite that the implication is stronger: that we can't have all
>> > of DMTBR, majority, and reversal symmetry. But the proof is probably a
>> > lot harder to find, too.
>> >
>> > So all of the above implies that when creating a resistant ranked
>> > method, we can't both have extreme resistance to burial and compromising
>> > - we have to pick one. Fortunately (as James Green-Armytage originally
>> > showed), we already get a great deal of compromising resistance from the
>> > Condorcet criterion itself (since, for instance, it does the right thing
>> > under center squeeze). Thus it's more sensible to choose further burial
>> > resistance over further compromise resistance if we can only have one.
>> >
>> > (Unless we consider maximum compromise resistance absolutely
>> > non-negotiable, e.g. Mike O's insistence on the FBC.)
>>
>> Well, insisting on weak FBC would rule out Condorcet. Maybe a better
>> example would
>> be my "Condorcet Compromise Extension":
>> votingmethods.net/cce
>>
>> This proposes a (convoluted) way to make use of the fact that in all
>> Condorcet
>> methods there are possible results under various scenarios that would
>> necessarily
>> create compromise incentive. So we can simply directly try to avoid those.
>>
>> As I've suggested before, I don't share the feeling that we should say
>> that
>> Condorcet inherently ensures adequate compromise resistance, and from
>> there try to
>> maximize burial resistance. I think the worst Condorcet methods wrt
>> compromise
>> incentive are to be sure not worth advocating.
>>
>> What I think instead is that voters will see burial under Condorcet as an
>> unattractive, excessively risky option provided that:
>> 1. voters have a natural inclination to truncate the options they like
>> less than
>> the best frontrunner (as opposed to ranking them sincerely, or using
>> burial). And
>> 2. truncation is an effective defensive strategy under the method.
>>
>> #1 I believe is just true. #2 we can certainly foul up. (Without #2,
>> offensive and
>> defensive strategy become indistinguishable: Burying the worse
>> frontrunner may not
>> be an attempt to steal a win, but to thwart someone else trying to steal
>> it.
>> Voters need to feel that truncation is a sufficient defense, so they
>> don't do
>> this.)
>>
>> I'm assuming generally that the way the burial strategy works is that A
>> voters
>> falsely rank non-viable candidate C over rival frontrunner B, and expect
>> that B
>> voters will prevent a disaster by reporting that A is better than C. But
>> I wonder
>> in what scenarios that is realistic to expect? Some will say it's a shame
>> if B
>> voters can't freely and safely vote B>A>C, as they really feel, but to me
>> it is a
>> luxury, when A vs B is the only real question to be answered in the
>> election.
>>
>> Kevin
>> votingmethods.net
>>
>
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