[EM] Instant Runoff Voting 3-candidate elections - pathologies considerably more common than you may have thought

[Jonathan Lundell]

On Aug 29, 2010, at 1:29 AM, Kristofer Munsterhjelm wrote:
> 
> Jonathan Lundell wrote:
>> On Aug 27, 2010, at 12:48 PM, robert bristow-johnson wrote:
>>> with Score and Approval, it's easy to mark your favorite candidate
>>> (Score=99 or Approval=1).  and we know that Satan gets Score=0 or
>>> Approval=0.  then what do you do with other candidates that you
>>> might think are better than Satan?  that question has never been
>>> answered by Clay.  and any answer must be of a strategic nature.
>> That is, to my mind, a fundamental problem with cardinal-rating
>> systems--approval, borda, range, etc. Except for some trivial cases
>> (notably two-candidate elections), the voting act is necessarily a
>> strategic exercise. With an ordinal method (IRV, Condorcet (though
>> one could I suppose specify a non-ordinal cycle breaker), Bucklin)
>> it's at least possible (and usually a good idea) to cast a sincere
>> ballot.
> 
> What do you think of Cardinal Weighted Pairwise? It uses a Condorcet matrix and sets the direction of defeats according to inferred ranking of the rated ballots, but the magnitude according to the rating. James Green-Armytage also suggests that a method that makes use of it normalize the ratings within the Smith set so the voters don't have to guess at what the Smith set will actually be.

I don't see how it cures the cardinal problem. 

> 
>> Why the latter is a good thing is a separate discussion... ---- 
> 
> I think Abd once argued that people will "automatically" vote in the Approval, maximum for all those I like better than the lesser evil, minimum for the rest, manner. IIRC, he called it "Neumann-van Morgenstern utilities".
> 
> I don't think so, so I think Approval burdens people with the need to be strategic, but there you go -- that's at least one person arguing that one should (and would) rather use strategic utilities.

The strategy problem isn't solved by recommending a "best strategy". I agree with you on the subject of Approval, merely point out that the same is true for any cardinal-weighted system.