[EM] Condorcet question - why not bullet vote

[Kevin Venzke]

Hi Peter,

My quick responses to this:

--- En date de : Mer 16.6.10, Peter Zbornik <pzbornik at gmail.com> a écrit :
>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.

None of this is guaranteed. Actually listing additional preferences can
also help a preferred candidate.

>Q: In this case why should any voter not bullet-vote?

You should not bullet vote if the possible use of voting for a second
preference outweighs the likelihood that the second preference will hurt
your first preference.

It is not obvious that a voter should be trying to support his favorite
candidate to the exclusion of everything else. He should be trying to
get the best result possible on average.

>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?

Yes, that can happen. But it doesn't follow from this, that everybody
should bullet-vote. If A and B are similar candidates then all of these
voters benefit from the A>B votes even though the B voters only voted
B and denied A chance to win. Most likely if the A voters bullet-voted
also, then some other candidate would win.

>... 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?

It could be rational in some cases, but it is not rational in general. In
general it makes sense to express your preferences.

Kevin Venzke