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

[Dave Ketchum]

On Sat, 9 Aug 2003 08:14:46 -0400 Eric Gorr wrote:

> 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


First you say "here is the example" - and then you present TWO UNEQUAL 
examples:
       You give B a solid win.
       Referenced example has B win via a cycle.

> 
> 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.


The referenced example is consistent with C being near to B, rather than 
being unique (if unique, likely some As would take an interest in C).

> 
> 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.


The example was presented by Markus Schulze, designed to give the results 
I described, when counting via BEAT PATH method.  Clearly you must have 
used a different method to get your different results.

I do not like declaring a tie, for we prefer declaring a winner without 
tossing a coin when at all possible.

Not clear to me whether an example can be constructed to make beat path 
look ugly - such ss making D MUCH preferred over A yet making A win via 
order of discarding pairs.

> 
> 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.
> 

Are you saying that six candidates tangled in cycles within a cycle is not 
odd - could be common in the books that discuss possibilities, but this 
many candidates contending this evenly in real voting looks odd to me.
-- 
davek at clarityconnect.com  http://www.clarityconnect.com/webpages3/davek
  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
            Do to no one what you would not want done to you.
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