[EM] "scored condorcet", etc

[Kevin Venzke]

Rob,

--- Rob Brown <rob at karmatics.com> a écrit :
> Kevin Venzke <stepjak <at> yahoo.fr> writes:
> > Actually plurality only fails half of it. Plurality isn't sensitive to
> > cloning losers.
> 
> Ok, well what plurality does with cloning winners is so bad that it
> results in
> the partisan stuff that we have today in Washington and elsewhere.

I don't think I would blame this on failing clone independence. If 
plurality could detect compromise candidates, I think that would be 
enough. (There are a number of methods that satisfy clone independence
which do not seem to me to be better than plurality here. Also, my own
favorite method is a "little bit" sensitive to cloning winners, but I
don't think it makes any difference in this area.)

> However, I'm still unable to picture the real world consequenses of
> minsum/dodgson's problems. Similar candidates would help each other, 

But this means that factions can deliberately nominate multiple candidates
solely because it may help, and can't hurt, assuming other voters ignore
the clones (rather than trying to do something strategic with them).

> as opposed
> to hurting each other as they do in plurality.  Since it requires a
> non-condorcet winner for this to even have an effect, how much of a real
> effect
> would this have?

Hard to say. But I don't think it's ever safe to expect that cycles 
will be rare.

My bigger complaints are that MinSum fails the plurality criterion (i.e.
MinSum can elect a candidate who has fewer votes in any position than
some other candidate has in first place) and minimal defense (i.e., if
more than half of the voters rank A, and leave B out of their ranking
entirely, MinSum can still elect B).

> The biggest question for me is whether a method would reduce (or
> eliminate) the
> ugly and destructive partisanship we see in government (at least in the
> US).  I
> don't claim to know how dodgson would compare to minmax or beatpath in
> that
> respect.  But that's what I'm more interested in knowing.

You have to decide what causes this partisanship, and then you can identify
criteria which address the problem. I'd say the problem is caused in
large part by the fact that only the two candidates most perceived to 
be viable can expect to receive votes.

The "favorite betrayal criterion" addresses this in that a voter is assured
that he can rank any number of candidates in the top position without fear
that his vote would be more effective in electing one of these candidates
if he had not included some of those candidates (i.e., less viable
candidates) at the top.

None of the methods you listed satisfy FBC, but beatpath(wv) was quite
good when I included it in some simulations.

> I have no problem with MinMax, I only explored MinSum, which I now see is
> called
> Dodgson, because I hadn't seen it discussed.  Minmax is fine.

(Just to say it again, I don't think MinSum should be called "Dodgson."
You can't find the Dodgson winner just from the pairwise matrix. You
have to count movement on the actual ballots. Summing the defeat margins
is just an approximation of this.)

Kevin Venzke



	

	
		
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