[EM] Condorcet question - why not bullet vote

[Peter Zbornik]

Hi Kristofer,

thanks for a detailed answer.
As you answer contingency, it might be beneficial to turn the question
around.
In what situations will bullet voting help my candidate to win (considering
the advanced Condorcet systems)?

Peter

On Wed, Jun 16, 2010 at 8:14 PM, Kristofer Munsterhjelm <
km-elmet at broadpark.no> wrote:

> Peter Zbornik wrote:
>
>> Dear all, dear Markus Schulze,
>>
>> I got a second question from one of our members (actually the same guy
>> which asked for the first time):
>> If I just bullet vote in a Condorcet election, then I increase the chances
>> of my candidate being elected.
>> If I have a second or third option, the chances of my prefered candidate
>> to win is lowered.
>> Q: In this case why should any voter not bullet-vote?
>> I have some clue on how to answer, but not enough for an exhaustive
>> answer.
>>
>
> I would say that the answer is contingency. Say that your favorite is A,
> and it's uncertain whether B or C is more popular, but you prefer B to C.
> Then, bullet-voting A might give you A instead of B (which would be good),
> but it might also give you C rather than B (which would be bad) because you
> falsely reported that it doesn't matter to you whether B or C wins.
>
> A bit more formally, consider this: C is the current CW and B is just short
> of beating him, while A is far behind. If two voters vote A > B = C, then
> nothing happens, but by voting A > B > C, B now beats C and wins.
>
> Also note that voting for additional candidates doesn't harm the outcome
> unless you, by doing so, set up or help others set up a cycle. If X is the
> CW and beats others by a lot of votes, then voting others ahead of X doesn't
> itself do anything harmful; the only potential for harm occurs in the domain
> of the cycle.
>
> Similarly, for the "advanced methods" (Schulze, Ranked Pairs, and so on),
> ranking candidates that end up outside of the Smith set doesn't do any harm
> either, because these methods satisfy Independence of Smith-dominated
> alternatives (also called "local IIA").
>
> To sum all of that up: bullet-voting is like driving straight in a game of
> Chicken. Sure, you might benefit by doing so, but you may also crash and get
> a very bad outcome. In addition, the advanced methods pass criteria that
> both narrow down the situations where sincerity will backfire, as well as
> the degree to which it would do so; an ISDA-compliant method must obviously
> elect from the Smith set in the first place, for instance.
>
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