[EM] More non-altruistic attacks on IRV usage.

[Kristofer Munsterhjelm]

robert bristow-johnson wrote:

> what do you mean: "weight"?  rankings are just rankings.  if a voter 
> ranks Candidate A above Candidate B (independent of what the absolute 
> rank values are), all that means is that this voter would vote for A if 
> it were a simple two-candidate race with B.  and all Condorcet seeks to 
> accomplish is to be consistent with that social choice regardless if 
> Candidate C or Candidate D were in the race or not.
> 
> it's pretty simple:
> 
> 1. if a majority of voters agree that Candidate A is a better choice for 
> office than Candidate B, then Candidate B is not elected.  this imposes 
> consistency with the 2-candidate race where we all agree who should be 
> elected and why.
> 
> 2. the relative merit of Candidate A to Candidate B is not affected by 
> the presence of a third candidate, C.  in the converse, this means that 
> removing any loser from the race and the ballot, that this should not 
> change who the winner is.  if it does, that loser is a "spoiler".  it is 
> precisely the motivation for adopting IRV in the first place.

To my knowledge, Condorcet passes IIA whenever there is a Condorcet 
winner. If Condorcet winners are frequent, that's a pretty good property.

That is, if candidate A is a Condorcet winner, and you remove some other 
candidate B, A is still the Condorcet winner. If you add some other 
candidate C, unless C beats A, A is also still the Condorcet winner.

Some may not like the tradeoffs Condorcet bring (like failing FBC), but 
it bears keeping in mind, I think. While IIA (general 
spoiler-independence, as it were) might be too strong to be sensible in 
the general case, having a method pass it in certain cases is welcome.

Advanced methods can go further, as well: a method that passes 
independence of Smith-dominated alternatives will not be influenced by 
candidates outside the Smith set.

(Of course, if there's rarely a CW or if the Smith set is usually large, 
this doesn't amount to much. Offensive strategy attempts to create 
cycles in the strategists' favor.)