[EM] CDTT,IRV (Chris)

Chris Benham chrisbenham at bigpond.com
Mon May 30 08:27:10 PDT 2005

(Sorry list about the double posting and pairwise matrix tables mess. I 
copied something from an on-line vote calculator which looked ok when I 
sent it.)
I  had written:

>Take this really outrageous scenario (one of James G-A's):
>> 46: A>B>C
>> 44: B>C>A   (sincere is B>>>>A>C)
>> 05: C>A>B
>> 05: C>B>A
>> A is the sincere CW, and the (voted) CDTT is {A,B,C}.  Pairwise 
>> Defeat-Dropper(Winning Votes)  elects the Buriers' candidate B, while 
>> CDTT,IRV easily elects A.
You responded (Fri.May 17):

>It's interesting. IRV manages this by eliminating C due to low first 
>preferences, whereas FPP and DSC favor the first-preference winner, who
>could predictably be the buriers'. CDTT,MMPO elects C, I believe.
A>C 90-10,    C>B 54-46,   B>A 51-49.   MMPO scores:   A51,   B54,   
C90.  The MMPO winner is the Burier's candidate B, not C.

Your other point is right.  We can slightly change the example so that 
the sincere CW isn't the FPP winner.

44: A>B>C
46: B>C>A         (sincere is B>>>>A>C) 
07: C>A>B
03: C>B>A

Again the sincere CW is A and again defeat-dropper (WV) elects the 
Buriers' candidate B; as does plain MMPO and CDTT,MMPO and  all the 
other reasonable deterministic
CDTT methods except  CDTT,IRV.

>It makes me wonder whether the IRV behavior could be duplicated without
>failing Mono-raise. (I'd prefer to fail Clone-Winner.)
I  can't say I share your preference, but that would be very interesting.

Chris  Benham

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