[EM] Condorcet question - why not bullet vote?

[Peter Zbornik]

Chris, thanks for pointing these things out. I didn't know about the
Later-no-Help.

You write: "But all Condorcet methods fail Later-no-Help, and in some this
effect is sufficiently strong for the method to have a "random fill"
incentive."
Do you know for which Condorcet methods this effect is sufficiently strong
to have a random fill incentive?

You write: "That means that if you know nothing about how other voters will
vote you are probabilistically better off by strictly ranking all your least
preferred candidates."
Is this claim possible to prove or is it at least supported by some
evidence?

As for the no info, equal rank - this is a rational strategy when you have
no info. In real life you have a lot of information about the expected
voting behavior of others.

Peter

On Wed, Jun 16, 2010 at 9:11 PM, Chris Benham <cbenhamau at yahoo.com.au>wrote:

> Peter,
>
> If I just bullet vote in a Condorcet election, then I increase the chances
> of my candidate being elected.
>
> Bullet voting in an election using a method that complies with the
> Condorcet criterion does I suppose
> somewhat increase the chance of your candidate being the Condorcet winner.
>
> But all Condorcet methods fail Later-no-Help, and in some this effect is
> sufficiently strong for the method
> to have a "random fill" incentive.  That means that if you know nothing
> about how other voters will vote
> you are probabilistically better off by strictly ranking all your least
> preferred candidates.
>
> 46: A>B
> 44: B
> 10: C
>
> Here A is the CW, but if the 44B voters change to B>C then Schulze(Winning
> Votes) elects B.
>
> Schulze (WV) also has a zero-info. equal-rank at the top incentive. So say
> you know nothing about
> how other voters will vote and you have a big gap in your sincere ratings
> of the candidates, then your
> best probabilistic strategy is to rank all the candidates in your preferred
> group (those above the big
> gap in your ratings) equal-top and to strictly rank (randomly if
> necessarily) all the candidates below
> the gap.
>
> Your question seems to come with assumption that the voter doesn't care
> much who wins if her favourite
> doesn't.
>
> Q: In this case why should any voter not bullet-vote?
>
> The voter might be mainly interested in preventing her least preferred
> candidate from winning. Bullet
> voting is then a worse strategy than ranking that hated candidate strictly
> bottom.
>
> Another Condorcet method is  Smith//Approval(ranking). That interprets
> ranking versus truncation as
> approval and elects the member of the Smith set (the smallest subset S of
> candidates that pairwise beat
> any/all non-S candidates) that has the highest approval score.
>
> (Some advocate the even simpler Condorcet//Approval(ranking) that simply
> elects the most approved
> candidate if there is no single Condorcet winner.)
>
> In the example above the effect of the 44B voters changing to B>C is with
> those methods to make C
> the new winner.
>
> Those methods do have a truncation incentive, so then many voters who are
> mainly interested in
> getting their strict favourites elected will and should "bullet vote".
>
> What is wrong with that?
>
> Chris Benham
>
>
>
>
>
>
> 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.    My argument starts:  If I vote for a candidate
> who has >50% of the votes, then it does not matter  if there is a second or
> third choice.  If my prefered candidate A gets <50%  of the votes, then it
> makes sense to  support a second choice candidate B.  However if the
> supporters of B only bullet vote, then maybe B's supporters  get an
> advantage over A?  ... at this point I realize, that I don't know enough
> about Condorcet and/or  Schulze to answer the question.    Why is it not
> rational to
>  bullet vote in a Condorcet election if you are  allowed not to rank some
> candidates?  I guess you have discussed this question a zillion of times, so
> please  forgive my ignorance.    Maybe you could help me out with this one.
>    Peter
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20100616/6f9a76ec/attachment-0004.htm>