[EM] Re: Issues, Condorcet, and IRV (was: IRV vs. plurality)

[Eric Gorr]

At 5:26 PM -0400 8/8/03, Dave Ketchum wrote:
>On Fri, 8 Aug 2003 11:08:30 -0400 Eric Gorr wrote:
>
>>At 3:03 AM -0400 8/8/03, Dave Ketchum wrote:
>>
>>>      Except for cases involving IRV spoilers, winners are 
>>>IDENTICAL - repeat IDENTICAL!!!
>>>  Condorcet backers emphasize the IRV spoilers because those are 
>>>the major reason for choosing Condorcet over IRV (Condorcet claims 
>>>simpler counting of votes as an additional advantage).
>>
>>
>>What do you mean by IRV Spoilers?
>
>
>Looked to me as the same thing as happens under Plurality:
>      In 2000, Gore backers griped that Nader got in their way in Florida.
>      Here, C backers got in the way of B getting an easy win in IRV.

Just for reference, here is the example again:

40:A>B>C      40:A
35:C>B>A  or  35:C>B
30:B>A>C      30:B

You have presented one interpretation, but it is not the only one, 
which considering it in a more generic form.

C could simply be a third, unique option, which was least liked by 
the broadest number of people.

I am certain there are several other potential spins one can come up 
with to explain these (I assume them to be) sincere votes.

>>I think it has already been shown that the winners between IRV and 
>>Condorcet are not identical in more then just these cases.
>
>
>I concede below that it can be other than odd cases.  As to odd cases:
>      Markus recently hit us with a demonstration that Condorcet can 
>be tortured into odd results with paper voters - and doing that 
>particular torture with real voters seems unbelievable:
>      Prospect was that A was winning, three more ballots turned up 
>with A in first rank, and these ballots caused D to win.
>      Method was to start with a particular method of resolving 
>cycles (nothing wrong with the method - just provides knowledge for 
>constructing the torture), provide a 6-member major cycle containing 
>two 3-member minor cycles, and define vote counts for two pairs 
>connecting the minor cycles such that lower ranks in the three odd 
>ballots will change which of these pairs is discarded first, and 
>thus which minor cycle contains the winner.
>
>     Turns out the three voters could have succeeded via bullet voting,
>BUT, for all they knew without the vote counts in front of them, could
>have happened that their lower rank votes were needed to let the A cycle
>contain the winner.

Here is that example again (in a form so it can be easily fed into my site):

4:A>B>C>D>E>F
2:A>B>F>D>E>C
4:A>E>B>F>C>D
2:A>E>F>B>C>D
2:B>F>A>C>D>E
2:C>D>B>E>F>A
4:C>D>B>F>E>A
12:D>E>C>A>B>F
8:E>C>D>B>F>A
10:F>A>B>C>D>E
6:F>A>B>D>E>C
4:F>E>D>B>C>A
3:A>E>F>C>B>D     - the extra three votes

According to my site, there is a tie between A & D with or without 
those extra three votes added. The reason is that when I consider the 
victories that form the minor cycles, those victories get rejected 
because they form cycles.

This clearly seems to be the right thing to do in this case as the 
voters have provided no clear information on how they feel between A 
& D.

This, unfortunately, does not appear to be an odd case.