[EM] Sincere methods

Tue Apr 26 14:14:19 PDT 2005

Juho,

 --- Juho Laatu <juho4880 at yahoo.co.uk> a écrit : 
> > It still makes no difference, since a method can't tell the two types 
> > of clones apart.
> 
> I think we agree on that. But since the true closes are not known, then 
> it may be as wrong to interpret all possible clones as members of one 
> party than it is to treat all of them as individual candidates. One 
> just doesn't know. And if one changes the winner based on a false clone 
> assumption, then one may violate the rights of the candidate that would 
> have won without the clone assumption.

I think this is kind of silly. What "rights" could be violated?

> >>> The thing that would change this, is if you want to argue that
> >>> sometimes
> >>> Smith or clone independence causes a worse candidate to be elected.
> >>> But I
> >>> don't think that's what you're saying.
> >>
> >> Actually I do. I don't know the clone world well enough to say 
> >> anything
> >> on that but I can make a claim on the Smith set. My claim is that
> >> minmax (margins) is a SVM.
> 
> > But I don't find your reasoning persuasive, since if there were 
> > hypothetically
> > the ability to obtain "additional votes" to create a Condorcet winner, 
> > then
> > why couldn't there be the ability for voters to alter their votes so 
> > as to
> > avoid the election of the Condorcet loser?
> 
> I agree that the "additional votes" are not something that would 
> materialize, they are just a tool for imagination when comparing 
> different outcomes of the election.

But my point is that, other than simplicity, I can't see why "additional votes"
gives more useful answers than some other imaginary experiment. A better argument
seems necessary to oppose Smith.

> > I can't remember if you and James used this scenario:
> >
> > 20 A>B>C>D
> > 20 B>C>A>D
> > 20 C>A>B>D
> > 13 D>A>B>C
> > 13 D>B>C>A
> > 13 D>C>A>B
> 
> Not exactly but close enough to serve as a good example.
> 
> > You could imagine that it would be slightly easier for the D voters to get
> > the additional voters necessary to make D the CW. But it seems to me easier
> > to imagine that the voters solidly committed to {a,b,c} would just compress
> > their rankings.
> 
> If there was a second round, A, B and C supporters would have an 
> interest to join forces against D. The needs of A, B and C supporters 
> would be served better. But needs of voters in general would be served 
> worse (if MinMax is used as the SVM). Better not tell to A, B and C 
> about this possibility :-). Maybe the voting method should not help 
> them implementing the strategy.

No, because the method should have the sense to see that this strategy is
what the ABC voters would attempt in a second round.

> If A, B and C are true clones and all belong to party "ABC", then the 
> situation changes a bit. We could expect that A, B and C are friendly 
> competitors and they now regret that they didn't arrange a pre-election 
> where one of A, B and C would have been elected as the only "ABC" party 
> candidate for the main election.

It is *bad* if candidates wish they had had a pre-election. The method should
not fail to work just because some candidates are added in.

I don't think it matters whether ABC are "true clones." Whether candidates
are considered "clones" is based on how the votes are cast. The ABC voters
don't have to cooperate with each other if the method has the sense to see
that {a,b,c} would beat {d} in a one-on-one election.

> If we do not elect D, we may violate one of the principles of basic 
> ranking based election, namely the fact that only relative preferences 
> should be considered, not their strengths. Vote A>B>C>D should mean 
> A>B, A>C, A>D, B>C, B>D and C>D and nothing more (not e.g. A>B>C>>>>D 
> which could be a good guess if A, B and C were true clones).

Eh? You don't need to make assumptions about preference strength to elect
from the Smith set.

> Let's assume for a while that A, B and C are false clones. I'll add 
> some sincere rating style information in the votes (">>>>").
> 
> 20 A>>>>B>C>D
> 20 B>>>>C>A>D
> 20 C>>>>A>B>D
> 13 D>>>>A>B>C
> 13 D>>>>B>C>A
> 13 D>>>>C>A>B
> 
> Now we have four separate parties. All voters like their own first 
> priority candidate but find all others really bad. Electing the 
> candidate of the largest party "D" doesn't look that bad any more. I'm 
> of course fighting against myself now when giving another chosen 
> meaning (separate party interpretation instead of the clone party 
> interpretation) to the votes. MinMax lies somewhere between these two 
> interpretations.

Of course with this interpretation, voters have no way to defeat D except
by lying about who their favorite is.

> Did I have any luck in trying to find arguments to justify the (so 
> neglected) MinMax as a sincere voting method?

I'm really not sure what this question means. What would justify MinMax as
a sincere voting method? Being "natural" and easy to explain, right? Then, sure,
I don't see why not. But I don't yet understand why such methods are 
interesting to consider.

> P.S. Note also the other example that I discussed with James. This one 
> doesn't have any clones, and A, B and C are not as likely to agree on a 
> joint best candidate.
> 101: A>B>X>C
> 101: B>C>X>A
> 101: C>A>X>B
> 100: X

X is on the wrong side of a majority in every contest. For that reason I
consider it contrary to the purpose of an election to elect X.

Kevin Venzke

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