[EM] Why I think IRV isn't a serious alternative

[Dave Ketchum]

On Tue, 25 Nov 2008 11:45:00 -0800 Jonathan Lundell wrote:
> On Nov 25, 2008, at 11:25 AM, Markus Schulze wrote:
> 
>> Dear Jonathan Lundell,
>>
>> Greg Dennis wrote (25 Nov 2008):
>>
>>> I've studied every IRV election for public office
>>> ever held in the United States, most of which have
>>> their full ranking data publicly available, and
>>> every single time IRV elected the Condorcet winner,
>>> something I consider to be a good, though not
>>> perfect, rule of thumb for determining the "right"
>>> winner.
>>
There have not been many IRV elections in the US.

For most elections the method does not matter much - even Plurality usually 
gets it right.

The ranking that IRV and Condorcet share matters.  Though they look for 
different aspects, they will usually agree since assuming that A>B, that is 
exactly what Condorcet counts, and that will encourage A toward A being a 
first choice, which is what IRV looks for.

Then look at the French election that made voters think of riots - runoffs 
were UNABLE to offer acceptable choices.  IRV can fail in the same way. 
Even though it cannot be expected often it will be most likely in an 
election fought bitterly by a bunch of candidates.

Couple minor notes about Condorcet's NxN arrays:
      They help toward verifying the counting being correct.
      Publishable,  they help see comparative liking of the candidates.
>>
>> I wrote (25 Nov 2008):
>>
>>> If I remember correctly, Abd wrote that, in every
>>> IRV election for public office ever held in the
>>> USA, the IRV winner was identical to the plurality
>>> winner. Doesn't that mean that -- when we apply
>>> your logic -- plurality voting always elects the
>>> right winner?
>>
It encourages the dream - but certainly does not make the dream true.

DWK
>>
>> You wrote (25 Nov 2008):
>>
>>> Plurality failed in Florida 2000, so we can conclude
>>> that "plurality voting always elects the right winner"
>>> is false.
>>
>>
>> And when you apply Abd's claim to your conclusion (that
>> the statement "plurality voting always elects the right
>> winner" is false), what can you conclude about Greg's
>> claim?
> 
> 
> Greg concludes that IRV, in practice, tends to elect the Condorcet  
> winner. Does he conclude that it must always be so? I don't think so.
> 
> Abd says that the IRV winner in these cases was also the plurality  
> winner. Again, no claim of necessity.
> 
> We might equally well conclude that plurality usually elects the  
> Condorcet winner, and that it fails infrequently enough that we don't  
> have examples of IRV correcting a plurality error. (Florida 2000 is an  
> example of a plurality error that IRV would most likely have corrected.)
> 
> 
> My own view is first that we're talking about marginal differences  
> here, and that PR vs single-winner elections is of much, much greater  
> interest, and second that the interesting difference between  plurality, 
> IRV and other ranked methods is not in how they count any  particular 
> profile, but rather in how they influence candidate and  voter behavior. 
> In the IRV examples that Greg and Abd adduce, we don't  actually know 
> what the ballots would have looked like if the elections  had used 
> plurality. The set of candidates might well have been  different, the 
> nature of the campaigns different, and voter strategies  different.
> 
> Given an IRV election, the question "how would this election have  
> turned out if plurality had been used" cannot be answered by counting  
> the IRV first choices.
-- 
  davek at clarityconnect.com    people.clarityconnect.com/webpages3/davek
  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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