[Election-Methods] RE : Re: RE : STV in the context of modeling voters

Kevin Venzke stepjak at yahoo.fr
Sun Dec 30 13:28:20 PST 2007


--- Jonathan Lundell <jlundell at pobox.com> a écrit :
> > I didn't quite understand your post... In the first part of your  
> > post you
> > seemed to be discussing the strategy of selecting the candidate you  
> > want to
> > win. It didn't seem you were discussing the voting strategy once you  
> > know
> > what you want. So how could this become easier when you're allowed  
> > to rank
> > the candidates (whether with a LNHarm guarantee or without)? Surely  
> > it's
> > harder to form a ranking than to pick a single favorite?
> I'm arguing otherwise, or at least that ranking N candidates on a  
> contingency basis is of difficulty O(N), while trying to rank on the  
> basis of quantifying and consolidating multidimensional preferences is  
> O(unquantifiably harder).

I must not be understanding you. I thought surely you would face the latter
problem no matter what election method you were using. Are you saying
plurality voting only requires the second, and IRV only requires the first?

> I'm also, at least implicitly, suggesting that the use of voter models  
> to evaluate election methods is interesting, but that the difficulty,  
> to the point of impossibility, of building and verifying such models  
> that reflect real-life voter behavior makes it problematical to draw  
> much in the way of conclusions.
> For example, someone recently pointed out that IRV elects the middle  
> of three candidates only 1/3 of the time, with a voter model based on  
> random distribution along a single dimension. I conclude that if I  
> ever have occasion to hold an election in such an environment, I might  
> or might not use IRV, depending on whether I had decided a priori that  
> the middle candidate was preferable (in which case I could suggest a  
> trivially simple algorithm for picking the winner).

If you have a trivially simple algorithm for electing the middle of three
candidates, and which doesn't come with strategic incentives that stop it
from working properly, I would love to hear what it is.

The reason why, in a one-dimensional setting, we might want to elect the
centermost candidate, is because this candidate should defeat each of the
other candidates head-to-head.

Alternatively, if utility of a candidate to a voter is posited to be
proportional to the proximity of the candidate to the voter, then the
centermost candidate should provide the greatest utility.

> And I'm suggesting that we know from experience that voters can and do  
> select a single winner, and that IRV builds on that by asking the  
> voter merely to do it iteratively.
> > --- Jonathan Lundell <jlundell at pobox.com> a écrit :
> >> And its implicit
> >> decision model conforms to something that I, as a voter, can make
> >> sense of. And in making my contingent choices, STV's later-no-harm
> >> property becomes important to me. Of course I'd like it to be
> >> monotonic, etc, but on *my* value scale, its advantages, in practice,
> >> outweigh its shortcomings--in practice.
> >
> > For me, even a totally strategy-free method would not be acceptable  
> > if I
> > could not stand to the side as an observer and agree that the method  
> > gave
> > proper results.
> I question the ability of any observer, in general and in principle,  
> to do any such thing.

That's very interesting. The MMPO method satisfies LNHarm like IRV, and
additionally has no favorite betrayal incentive. The only problem is that
it has scenarios like this:

1,000,000: A
2: A=C (ranked equal)
2: B=C
1,000,000: B

MMPO elects C. Can you find any basis on which to criticize this result?

It's hard for me to imagine that an analyst might *only* value the
strategic incentives (or lack of) of a method, and not be concerned with
any qualities of the outcome. Personally I want to reduce strategic
incentives *in order to* improve the outcome.

Kevin Venzke

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