[EM] : Chicken problem (was: SODA and the Condorcet

[fsimmons at pcc.edu]

Jan,

IRV elects C like all of the other methods if the B faction doesn't truncate.  But IRV elects A when the B 
faction truncates.  Of course, with this knowledge, the B faction isn't likely to truncate, and as you say C 
will be elected.

The trouble with IRV is that in the other scenario when the B faction truncates sincerely because of 
detesting both A and C, IRV still elects A instead of B.

> Date: Sat, 6 Aug 2011 11:46:12 -0600
> From: Jan Kok 
> To: Jameson Quinn , Election Methods Mailing
> List 
> Subject: Re: [EM] Chicken problem (was: SODA and the Condorcet
> criterion)
> >>> To review for other readers, we're talking about the scenario
> >>>
> >>> 48 A
> >>> 27 C>B
> >>> 25 B>C
> >>>
> >>> Candidates B and C form a clone set that pairwise beats A, 
> and in fact C
> >>> is the Condorcet Winner, but
> >>> under many Condorcet methods, as well as for Range and 
> Approval, there is
> >>> a large temptation for the
> >>> 25 B faction to threaten to truncate C, and thereby steal 
> the election
> >>> from C. ?Of course C can counter
> >>> the threat to truncate B, but then A wins. ?So it is a 
> classical game of
> >>> "chicken."
> >>>
> >>> Some methods like IRV cop out by giving the win to A right 
> off the bat,
> >>> so there is no game of chicken.
> 
> Wait a minute! IRV elects C in this scenario, if that is how the
> voters actually vote, and those are the sincere preferences (A voters
> have no preference between B and C).
> 
> Much as I hate to say it, IRV works OK in that scenario. On the other
> hand, if the A voters prefer B over C, (as in the 2009 
> Burlington, VT
> mayoral election, http://scorevoting.net/Burlington.html) IRV ignores
> the preference and still elects C, which seems to be the wrong choice.
> 
> 
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