[EM] Condorcet question - why not bullet vote

[Jameson Quinn]

2010/6/16 robert bristow-johnson <rbj at audioimagination.com>

>
> On Jun 16, 2010, at 1:30 PM, 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 there is a Condorcet Winner (CW), the answer is "no".  If there is no
> CW, then we have a "Condorcet paradox" or a "cycle" where Candidate Rock
> beats Candidate Scissors, Candidate Scissors beats Candidate Paper, and
> Candidate Paper beats Candidate Rock.  Then I won't say whether the answer
> is "no" for sure, but I am still convinced that cycles are rare and that a
> method like Schulze or Ranked Pairs resolves the cycles meaningfully.


Would that it were this easy. But there could be an honest CW, and bullet
voting creates an artificial cycle.

Simple case:
40 C>B>A
30 B>A>C
30 A>B>C

B is the clear CW: wins 60/40 against C, and 70/30 against B. But if the A
voters bullet vote, then there is a Condorcet cycle, because now B loses
30/40 against C.

Some tiebreaking methods deal with this situation better than others. But if
they twist themselves up in enough knots to avoid this problem, then they
give results which are very hard to defend if half the A voters were really
A>C>B voters who truncated lazily.

Anyway, you cannot give simple guarantees like the one you stated above.

JQ
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20100616/f6fee19d/attachment-0004.htm>