[EM] minmax is not a good public election method

Kevin Venzke stepjak at yahoo.fr
Tue May 31 14:51:40 PDT 2005


--- James Green-Armytage <jarmyta at antioch-college.edu> a écrit :
> >Despite those criteria, I consider IRV to be less majoritarian than MM(wv)
> >or MMPO, since IRV can't even respect majority preferences with three
> >candidates. That is a bigger failing than MMPO failing mutual majority.
> 	Maybe MMPO is better than IRV; I'm not sure. But IRV does pass a number
> of significant criteria that MMPO fails, which means that MMPO is on shaky
> ground at best.

IRV has MMC (which doesn't really guarantee much), "Condorcet Loser" (which
doesn't really guarantee much), and Clone Independence, which I agree is
nice. In return, one gets from MMPO FBC, monotonicity, and Woodall's 
"Condorcet(gross)." In the three-candidate case, one also gets MMC, Minimal
Defense, and Participation.

> 	My point is that as long as you are in a political climate that will
> welcome a pairwise count method, you should choose a good pairwise count
> method, one that at least passes Condorcet, Smith, MMC and CL. These
> failures of MMPO are an absolutely unnecessary liability.
> 	If A beats B, and B has absolutely no beatpath to A, then in my opinion
> no good pairwise count method will elect B.

I suggest using CDTT,MMPO instead, then, so that MMC is satisfied. I don't
agree that even weak defeats need to be acknowledged, particularly if
something else is gained by it, such as LNHarm.

> Kevin:
> >This is very pessimistic. If minority voters have enough coordination to
> >vote insincerely *in a cycle*, surely the majority voters have enough 
> >coordination to simply not rank those candidates strictly!
> 	I grant you that. However, such counterstrategy would of course distort
> voter preferences. Also, it is possible that an MMC failure in MMPO could
> occur as a result of simple bad luck. Is this likely? Probably not. But
> again, my point is that the liability is clearly unnecessary. My
> near-supermajority MMC failure example is an extreme one. Smaller mutual
> majorities can be thwarted by cycles that are less improbable.

That is barely true. Any example needs a majority-strength cycle.

> 	So, in choosing MMPO instead of something like beatpath, you are willing
> to trade Condorcet, Smith, MMC, CL, and IC for later-no-harm and what I
> call elimination of compromising-reversal incentive (and you call FBC). I
> don't know if I can change your mind about this, but at least I can voice
> my opinion that this is a very misguided trade.

I wonder if you realize how related those five criteria are.

I'm not at all sure I would suggest MMPO rather than Schulze. I would base
it on what the voters find more palatable.

> 	Why do you think later-no-harm is so important?

Because it gives voters the ability to safely rank all of their preferences. 
It reduces defection incentive (that is, defection by truncation). And as
a result, it is more likely that MMC will be satisfied in practice.

> 	As for getting rid of compromising-reversal incentive I think that it's
> enough to reduce it to an acceptable level while satisfying other
> important criteria like Smith. For example, compromising-reversal
> incentives in beatpath(WV) and beatpath(CWP) are extremely minor and
> occasional. Eliminating this minor and occasional incentive is not worth
> throwing over these important criteria.

I'm not sure about this. What if you don't expect that your favorite candidate
will win? Then ranking him above or equal to your compromise choice can do
little other than frustrate your compromise's ability to be elected.

Kevin Venzke


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