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

[Kristofer Munsterhjelm]

robert bristow-johnson wrote:

> i just think that the strategy of swinging an election from the 
> Condorcet winner into a cycle is just a risky strategy.  you never know 
> who will come out on top; your worst enemy might just as well as the 
> centrist may or as well as your candidate.  with something like Schulz 
> (or Ranked Pairs which does not result in a different candidate with a 
> Smith set of 3, and bigger than 3 seems to me even more unlikely than 
> that of getting a cycle anyway), you are emphasizing more decisive 
> elections in settling the ambiguity of a cycle.
> 
> say Ranked Pairs was the law, what kind of realistic strategizing can a 
> party or group of candidate supporters do? that example of tossing a 
> close election between RC (for radical center) and M (the centrist 
> candidate who is also the Condorcet winner if sincere ballots are cast) 
> is, in my opinion, too contrived to be a secure strategic guidance.  any 
> strategy that can just as well backfire, is no strategy.

The usual "nightmare" scenario for Condorcet goes somewhat like this:

Say you have three contenders (A, B, C) as well as mostly-unknown 
candidates D...Z.

The A camp says: "we need to pile candidates up on B and C so they won't 
win". Thus they vote A > D...Z > B = C.

The B camp says: "we need to pile candidates up on A and C so they won't 
win". Thus they vote B > D...Z > A = C.

The C camp says: "we need to pile candidates up on A and B so they won't 
win". Thus they vote C > D...Z > A = B

A few others (minor candidate supporters) vote D...Z > ...

Then a mediocre candidate, say D, wins.

In short, if everybody goes on a burial spree, Condorcet methods fail. 
It's not too realistic, although Warren disagrees 
(http://rangevoting.org/DH3.html ). It's probably more likely with Borda 
because Borda is centrist biased and can even fail Majority.