[EM] MAM vs Schulze

[Michael Ossipoff]

(Replying farther down)

On Oct 9, 2016 5:47 AM, "C.Benham" <cbenham at adam.com.au> wrote:
>
>
> Mike,
>
> When it comes to Condorcet methods, I think that  (up to a point) some
truncation incentive  (and so some "vulnerability to
> truncation") is somewhere between a good thing and a relatively small
necessary evil  ("necessary" to avoid greater evil).
>
>
>> The strategy situation of the methods you listed isn't as good as
Bucklin.
>>
>> Surely the purpose of a pairwise-count method is to _improve_ on Bucklin.
>
>
> C: The methods I listed all meet Smith and Bucklin doesn't.   Under
Bucklin all voters have such a strong truncation incentive that
> the method is more-or-less strategically equivalent to Approval.

(endquote)

Yes. ...unless you're at least fairly sure that you're majority-favored, in
which case you benefit from Bucklin's MMC.

Bucklin isn't fancy, complex or deluxe. It's just solid & reliable, like
Approval, on which it's based.

But yes, I'd rather just have Approval. But there may be many voters who
need it want rankings or MMC.

But it might often be difficult to know if you're majority-favored (& thus
in a position to benefit from MMC).

Because not everyone is MF (majority favored), I'd just prefer Approval.

Regarding that truncation incentive to which you refer:

That's how the CWs's voters can protect the CWs's win.

But it doesn't help in Benham, Woodall, or Margins-Sorted LV Elimination.

With those methods, the only way for the CWs's preferrers     to protect
hir from burial or truncation, us the probabilistic strategy that I
described.

That's why I said that those methods' strategy situation is worse than that
of Bucklin.

> Under Benham and  LV(erw) SME  informed strategists have a much weaker
truncation incentive and in the zero-info. case there
> is no truncation incentive.

With 0-info, use Approval, & approve your top-set. In fact, do so anyway,
because predictive information is unreliable.

>
> Given that burial vulnerability is unavoidable in Condorcet methods, I
think that is more democratic if  (in this respect) larger factions
> have the advantage over smaller factions.

I'll check out your example.

>
> 43: A
> 03: A>B
> 44: B>C  (sincere is B or B>A)
> 10: C
>
> C>A  54-46,    A>B  46-44,   B>C 47-10.
>
> Here A is the sincere CW and supported by the largest of the three
factions of voters, but Winning Votes rewards the buriers by electing B.
>
> Benham and  LV(erw)SME   easily elect  A.    Smith//Approval elects C.
>
>
>> Smith//Approval shares the great vulnerability to truncation & burial.
>
>
> C: Obviously the supporters of the sincere CW have much less truncation
incentive under Smith//Approval than they do under Bucklin,
> so  I wonder what example you have in mind.

Any example in which the CWs is truncated from one side.

>
> 40: A>B
> 35: B
> 25: C
>
> The Condorcet winner is  A, but under Bucklin the A supporters' failure
to truncate gives the win to B.

Yes, Bucklin is a simple, solid Approval method, whose strategy involves
truncation.

WV & MMPO try for better, by making the truncation not always necessary.
Maybe those methods won't have the perpetual burial fiasco.

The methods you describe need a lot more than defensive truncation.

Michael Ossipoff
>
> Chris Benham
>
>
>
>
> On 10/9/2016 7:50 AM, Michael Ossipoff wrote:
>>
>>
>> On Oct 8, 2016 6:06 AM, "C.Benham" <cbenham at adam.com.au> wrote:
>> >
>> > Mike,
>> >
>> > As far as I can tell, for all intents and purposes  MAM,  Schulze,
River and  Smith//MinMax (wv)  are all just different wordings
>> > of the same method.
>>
>> No. They sometimes choose different winners.
>> >
>> > If you think that MAM  is better than Shulze, then what criterion
(that we might care about) is met by MAM and not Shulze?
>>
>> Sometimes they choose the same, sometimes they don't.
>>
>> When they don't, the MAM winner is publicly preferred to the Schulze
winner several times more often than vice-versa.
>>
>> (It seems to me that it might have been something like 4 to 1, or 5 to
1. Steve Eppley would be the one to ask.)
>>
>> So: Choose in keeping with public preference, or contrary to it. Your
choice
>>
>> MAM's brief, natural & obvious definition is the opposite of the
arbitrary definition of Schulze or CSSD.
>>
>> MAM's definition clearly is the one that doesn't unnecessarily disregard
a defeat.
>>
>> It disregards a defeat only it's the weakest in a cycle with defeats for
which there  _isn't_
>> justification to disregard them.
>>
>> And, as I said, it's no surprise when unnecessarily disregarding defeats
results in a winner to whom the public prefer the MAM winner.
>>
>> >
>> > Or perhaps you have some example in mind where you think the MAM
winner is much prettier than the Schulze  winner?
>>
>> Publicly-preferred is prettier.
>>
>> Minimally disregarding defeats only with obviousl, strong justification,
never unnecessarily disregarding a defeat--That's prettier.
>>
>> >
>> >
>> >> MAM's brief definition just says:
>> >>
>> >> A defeat is affirmed if it isn't the weakest defeat in a cycle whose
other defeats are affirmed.
>> >>
>> >
>> > C: Is that definition fully adequate?
>>
>> Yes.
>>
>> You wrote:
>>
>> It doesn't tell you where to start.
>> >
>>
>> It isn't a procedural definition or a count-instruction. It's a brief
recursive definition.
>>
>> Given a set of rankings, it fully and definitely specifies a set of
affirmed defeats, & a set of not-affirmed defeats.
>>
>> ...and fully specifies the winner.
>>
>> For a procedure:
>>
>> Write down the strongest defeat.
>>
>> Below it, write down the next strongest defeat.
>>
>> Below that, write down the next strongest defeat, if it doesn't cycle
with defeats already written down.
>>
>> Repeat the paragraph before this one, until all the defeats have been
considered as described in that paragraph.
>>
>> A candidate wins if s/he has no written-down defeats.
>>
>> (end of count instruction)
>>
>> >> So, if it will be rare for them to differ, does that mean that we
should propose the more complicatedly-worded, elaborately- worded one?
>> >>
>> >> ...the less obviously, naturally and clearly motivated & justified
one?
>> >>
>> >
>> > C: Recently you accepted that  Winning Votes  is at best "maybe a bit
questionable", so why do you think that we should "propose" either?
>>
>> (endquote)
>>
>> I said they might be iffy or questionable. I didn't say they're ruled
out.
>>
>> For that questionable-ness, you get a chance for much better strategy.
>>
>> ...at the cost of the possibility of the strategic mess of the
perpetual-burial fiasco.
>>
>> I'd say that MAM, Smith//MMPO, & plain MMPO are worth a try.
>>
>> They should be included in a proposal that lists a number of suggested
methods.
>>
>> In particular, for an unlimited-rankings method, Plain MMPO offers the
most, for current conditions.
>>
>> >
>> > If  you want a Condorcet method that meets  Chicken Dilemma then I
prefer both "Benham"  and  Losing Votes (erw) Sorted Margins Elimination.
>>
>> (endquote)
>>
>> They're far too vulnerable to truncation & burial.
>>
>> In WV & MMPO, truncation just doesn't work. The CWs still wins.
>>
>> The strategy situation of the methods you listed isn't as good as
Bucklin.
>>
>> Surely the purpose of a pairwise-count method is to _improve_ on Bucklin.
>>
>> In Bucklin & Approval, the CWs's preferrers can protect hir win by
plumping.
>>
>> In Benham, Woodall, & Margins-Sorted LV Elimination, the best they can
do is:
>>
>> Say it's Worst (W), Middle (M), & Favorite (F).
>>
>> M is the middle CWs.
>>
>> The M voters could estimate or look up the expected sizes of the W & F
factions.  ...& rank one over the other probabilistically, so that each
one's probability of pair-beating the other is 50%.
>>
>> ...so that burial has a 50% chance of backfiring.
>>
>> In Bucklin, WV or MMPO, they need merely to plump.
>>
>> Or the F voters could rank M alone in 1st place. That would work in IRV
too (nothing else would).
>>
>> As I said, surely the purpose of a pairwise-count method is to _improve_
on Bucklin.
>>
>> >
>> > If you want a method that (like WV) meets Minimal Defense then I
prefer Forest's  "Max Covered Approval"  (which would nearly always be
equivalent
>> > to Smith//Approval, which I also like.)
>>
>> Smith//Approval shares the great vulnerability to truncation & burial.
>>
>> Michael Ossipoff
>> >
>> > Chris  Benham
>> >
>> >
>> >
>
>
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