[EM] Strategy-free criterion

[Kevin Venzke]

Hi Chris,

> Kevin,
> 
> > Who in 49/24/27 ranks a candidate below the less-liked frontrunner?
> No-one, which is why any method that meets SD and Plurality  must elect B.
> 
> > MD basically says that if there are two frontrunners and everyone truncates
> > their
> > less liked frontrunner, then the worse frontrunner won't win.
>
> "Truncates"  X means vote no-one below X.

In that case I mean "truncate above X but below the other frontrunner."

> > If this property doesn't hold, it means the majority has done something to stop
> > the method from
> > "seeing" their majority, which is surely that they ranked other candidates above
> > the preferred frontrunner.
> 
> But here you talk about "ranked other candidates above" which has
> nothing to do with truncation.

Truncation is what MD requires for it to work, but the problem it's usually
addressing is compromise. Every method that violates MD in 49/24/27 violates it
because of C being ranked above B. Betray C and there is no more issue. That's
bad, and MD wants to offer a way to fix it.

If MD fails to work because voters fail to truncate, that's not a violation of MD.

> That sounds more like failure of Non-Drastic Defense (which says that if
> more than half the voters vote X above Y and X no lower than equal-top
> then Y can't win.)

NDD is a weaker form of MD that does less to counter compromise.

> > In such a setting I find that MAMPO is usually not as good as MDDA or RMPA, but
> > all of them outperform all Condorcet methods at sincere Condorcet efficiency.
> 
> That's great.  Does that mean that you find  failure of Mono-add-Plump acceptable?

Compared to Plurality criterion failures, sure.

I don't really want to prejudge methods based on criteria that might primarily be
important for marketability reasons. I say "primarily" not "purely."

Hypothetically if there were a movement promoting MDDA, and in this world MDDA
doesn't violate the Plurality criterion, then Mono-add-plump failures wouldn't stop
me from supporting that movement.

And really, if I found that the whole world was actually OK with Plurality
failures, I might relax my stance on that as well. Because the marketability aspect
of Plurality failures is a big part of my allergy to them. Maybe I would study
under what conditions MDDA would have high risk of violating Plurality, and see if
I could live with it.

Kevin
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