[EM] Scenario where IRV and Asset outperform Condorcet, Range, Bucklin, Approval.

[robert bristow-johnson]

On May 12, 2010, at 3:22 PM, Jameson Quinn wrote:

> First off, I'm not generally an IRV advocate. But in the interests  
> of fairness, I think that the following (to me very plausible) 4- 
> candidate scenario should be considered.  I call it Radical Center,  
> in honor of Thomas Freidman's onanism. I'll present preferences, but  
> you can make this work with Approval (and thus also strategic Range  
> or Bucklin) using reasonable assumptions. In Approval and related  
> systems, there is a safe defensive strategy; in Condorcet systems,  
> if both relevant groups use strategy, neither wins and the whole  
> society is stuck with significantly inferior candidate.
>
> Candidates are Left, Right, Moderate, and the eponymous Radical  
> Center.
>
> Honest preferences (6 voter groups split into 3 larger groups for  
> easy understanding.)
> ---(35 L>...>R leftists)---
> 18: L>M>RC>R
> 17: L>RC>M>R
>
> ---(30 ...>L=R centrists)---
> 16: M>RC>L=R
> 14: RC>M>L=R
>
> ---(35 R>...>L rightists)---
> 18: R>M>RC>L
> 17: R>RC>M>L
>
> Condorcet winner is M. But if all the RC>M voters truncate before M,  
> then M does not beat R and L, so there's two cycles M>RC>(R|L)>M.  
> Most Condorcet tiebreakers, including Schulze and Minimax, would  
> name RC as the winner. (Of course, if the M voters retaliate in  
> kind, then R or L would win Condorcet, or M would win Approval,  
> Range, or Bucklin.)
>
> There are two ways I can see to avoid this dilemma.

i'm curious to exactly what is the dilemma.  it's pretty close between  
RC and M.  M is only barely preferred over RC.

is it that if M and RC voters voted against their political interests,  
then someone not to their liking gets elected?  (i can't even tell if  
it would be L or R, they look like they would tie.)  then the lesson  
is, if you don't vote for candidates (even if not your favorite) that  
represent your political interests, your political interests lose.

is it that if somehow the RC voters, that cannot see into the future,  
somehow take a risky guess and announce to their caucus to stick it to  
M, that they get rewarded for it?  or that the M voters hear about it,  
retaliate, and both groups get screwed?  how is the latter worse than  
what happens in plurality where there are more centrists than anyone,  
but they're in two rival parties, and they can't get their act together?

i haven't figgered it out yet, but are you saying that IRV would *not*  
reward the RC strategy and elect M anyway?

just curious.

--

r b-j                  rbj at audioimagination.com

"Imagination is more important than knowledge."