[EM] Condorcet How?

[Juho]

On Apr 12, 2010, at 3:57 AM, I wrote:

> On Apr 11, 2010, at 7:25 PM, Kevin Venzke wrote:
>
>>>> 49 A
>>>> 5 B
>>>> 19 B>C
>>>> 27 C>B
>>>>
>>>> It remains bad. I can't see what criticism would
>>> remain of this, other
>>>> than saying that in a real election we might be lucky
>>> enough to have
>>>> some A voters vote A>B and accidentally give the
>>> election away.
>>>
>>> I'm not quite sure that B should win with this set of
>>> votes. Note e.g. that the sincere opinion of the five "B"
>>> voters could be "B>C", and then this example says that
>>> with WV it is ok if those five voters truncate strategically
>>> and B wins instead of C.
>>
>> Yes, it is okay, because B voters should hardly be able to expect  
>> that
>> they will get full support from C.
>
> In this scenario I'd use another explanation. B and C are from left  
> wing parties that always support each others and rank the right wing  
> candidates (A) last. This time the election will be arranged using  
> WV. B supporters note that they can win by not supporting C any  
> more. C supporters do not have the same incentive since they are  
> about to win. Truncation is also useless as a counter strategy. In a  
> large public election it is probable that also others than B  
> supporters will know about this strategic opportunity and plan.  
> Candidate B could recommend sincere voting to his/her supporters, or  
> maybe not. But many B supporters might vote strategically anyway. C  
> supporters could truncate but that would be just a revenge that  
> could elect A instead of B. The dilemma is thus that B and C could  
> agree before the election that they will recommend sincere voting  
> and the candidate with more support would win (if left has more  
> votes than right), but they can not control the most eager B  
> supporters, and also B might be happy if some of the supporters will  
> truncate. The situation is unstable. If B wins the election with the  
> help of the truncating voters, what can we do before the next  
> election? Maybe change the method. Maybe try to convince all voters  
> that sincere voting is the best approach for all.

Here's one addition to the story. WV has been defended by saying that  
it is a benefit of WV that defensive truncation is possible. In this  
example the C supporters could spread word that they plan to truncate  
in any case (and vote 27: C). This approach would make the strategy of  
B voters useless in the sense that the risk that truncation of the B  
voters (5: B instead of sincere 5: B>C) would elect A increases. This  
approach has however some problems like requiring C voters to be  
strategic (and also in a way vote against their closest ally). The end  
result is also very unstable if B and C are about equally strong since  
then both could claim to be the leading candidate within the left wing  
and both recommend truncation (=> A may win). Some supporters of both  
of them may truncate for any of the reasons (attack, defence, revenge).

Juho