[EM] Defensive strategy for Condorcet methods KM

[Jameson Quinn]

2011/6/16 Kristofer Munsterhjelm <km_elmet at lavabit.com>

> Kevin Venzke wrote:
>
>  er... Is this right? I thought your penalty in the 3c case would have
>> to be just a single candidate's first preferences.
>>
>> I think I am probably right here. If you draw a triangle with ABC,
>> you have two cycle possibilities. In both cycles IRV elects the winner
>> between A and B. And in both cycles, that same candidate is beaten
>> by the "FPL" C.
>>
>
> I'll just have to say oops again. I'm not very well acquainted with cycles,
> and it shows :-) If you have A>B>C>A, then C isn't beaten by both A and B,
> because if that was the case, who would C be beating? Instead, C is beaten
> by B and beats A. So the penalties are
>
> for A: f(C)
> for B: f(A)
> for C: f(B)
>
> Doesn't that mean A must win, since C is the candidate with the least FPP
> votes?
>
> And if we have A>C>B>A, then
>
> for A: f(B)
> for B: f(C)
> for C: f(A)
>
> and B wins?
>
> Which I suppose is what you're saying.
>
> At least I know that this equivalence won't be the case for more than three
> candidates, because IRV isn't summable and FPC is.
>
> In an earlier post, Jameson said that the compromise strategy is too
> obvious for FPC in something like the Gore-Nader-Bush scenario. If FPC is
> C//IRV in the three-candidate case, does that similarly indict C//IRV, or
> does C//IRV seem complex enough that the voters don't see that?
>

Let me be clear that in a generic center-squeeze scenario such as
Gore/Bush/Nader, there is an honest CW, and so both FPC and C//IRV get the
"right" answer with honest votes (unlike plurality or IRV). Thus, if the
"Nader" (weaker extreme) voters decided to use favorite betrayal strategy in
FPC or C//IRV, it would be as a defense against burial by the "Bush"
(stronger extreme) voters. This is a valid defensive strategy in both cases,
but I do think that FPC's not-explicitly-Condorcet rules do make this
strategy more obvious than with C//IRV, especially to voters accustomed to
plurality.
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