[EM] Advantages of the two-round system vs Schulze method and contingent voting

[Kristofer Munsterhjelm]

Peter Zbornik wrote:
> Hi Kristofer,
> 
> thanks,
> 
> so is it right to state, that:
> 
> "The only advantage of Contingent vote before Schulze in terms of 
> satisfied criteria is in the case of three candidates, where the 
> Contingent vote satisfies Later-No-Harm"?

It's not exhaustive; my point is that Contingent vote in the three 
candidate case is like IRV. Thus, the criteria that Contingent possesses 
and Schulze does not is exactly equal to those that IRV does and Schulze 
does not - in the three-candidate case.

Other criteria IRV passes are: Plurality, Independence of Clones (if the 
correct tiebreaker is used), Later-no-Help, Condorcet Loser, and Mutual 
Majority.

Schulze fails both the LNH criteria (Later-no-Harm and Later-no-Help). 
It passes Plurality, clone independence, CL, and MM.

IRV is also resists Burial strategy to a greater extent than do 
Condorcet methods. Some Condorcet methods are particularly good at 
resisting burial (BPW, Smith,IRV, first preference Copeland) as far as 
Condorcet goes, but to my knowledge, they are still more susceptible to 
that than IRV is.

In any case, if you're going to go down the simulated runoffs path, I 
think IRV beats Contingent vote in all respects but summability. I 
further think that going in the Condorcet direction would be preferrable 
to trying to simulate runoffs..