[Election-Methods] Challenge: Elect the compromise when there're only 2 factions

[heitzig-j at web.de]

Dear Rob!

It is possible (otherwise I would not have posted this challenge :-)

But of course it is not possible with a majoritarian method (that's what you observed).

Keep on, one of the possible solutions is really simple (though not very good in other respects)...

> -----Ursprüngliche Nachricht-----
> Von: "rob brown" <rob at karmatics.com>
> Gesendet: 22.08.07 21:43:36
> An: 
> CC: election-methods at lists.electorama.com
> Betreff: Re: [Election-Methods] Challenge: Elect the compromise when there're only 2 factions

(temporarily exiting lurk mode since this one grabbed my attention)
> 
> I don't think it's possible, assuming the voters know what other voters' preferences are, and that they know that the other voters have the same information and will also vote optimally.
> 
> 
> The 55% in the first group will know that candidate B will never win, period.  So they have no incentive to compromise.  Since they don't have to worry about B, their only motivation is to make sure A, not C, wins, and any deterministic system will allow them to do just that.
> 
> 
> Howard's suggestion, that you prevent them from knowing other's preferences, is the only way it could select C.  But that is unrealistic and inherently unstable in the real world.
> 
> -rob
> 
> 
> On 8/21/07, Jobst Heitzig <heitzig-j at web.de> wrote:
> A common situation: 2 factions & 1 good compromise.
> 
> The goal: Make sure the compromise wins.
> 
> The problem: One of the 2 factions has a majority.
> 
> A concrete example: true ratings are
>    55 voters: A 100, C 80, B 0
> 
>    45 voters: B 100, C 80, A 0
> 
> THE CHALLENGE: FIND A METHOD THAT WILL ELECT THE COMPROMISE (C)!
> 
> The fine-print: voters are selfish and will vote strategically...
> 
> Good luck & have fun :-)
> 
> Jobst
> 
> 
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