[EM] Defeat Strength Demystified

[Kevin Venzke]

 Hi Forest,
A few extra thoughts.

    Le mercredi 15 septembre 2021, 23:09:57 UTC−5, Forest Simmons <forest.simmons21 at gmail.com> a écrit :  
>Once I became aware of this point of view, I saw the futility of Borda's assumption of honest voters, and the irrelevance of 
>Saari's appeal to geometric symmetry in Borda's defense. Also it made it more obvious why the standard use of Cardinal >Ratings/Score/Range/Grade ballots might just as well be replaced by simple Approval, since they all have the same optimal>strategy ... only the naive voter would vote strictly between the extremes. 
>
>After this point of view soaked in ... the defeat strength debate started to make more sense. In fact, a paramount ranked>voting strategy problem is the insincere "burial" of a second choice to give added support to a first choice. This problem is>especially evident in pairwise methods like Borda and Condorcet. But this kind of attack against a sincere Condorcet candidate>is easier to defend against when defeat strength is measured by winning votes.>
>Once this fact soaked in to my newbie psyche, I saw the wisdom of the Ossipoff camp with its impressive array of defense>criteria based on winning votes.
I think it was confusing and unhelpful that these criteria were usually explained in the context of burial.A criterion like SDSC (Strong Defensive Strategy Criterion) can really be viewed as a guarantee forcertain voters that compromise will not be needed, much like FBC. Some methods satisfying SDSC don'teven have burial, yet the property is not irrelevant. Implicit Approval on rank ballots is an easy example,or Bucklin.
It certainly seems like I am the last member of the "Ossipoff camp." What I would say is that WV itselfdoesn't matter. Only its practical implications matter. Minimize spoilers, minimize people regretting thatthey voted for their favorite candidate. People use such arguments to argue for Condorcet itself. Whytoss them out when choosing how to resolve a cycle?
>
>Eventually Mike O. went on to bigger and better things but a few years ago he made a brief, but passionate, return to the EM>List when the Possibilities of Hope seemed to include a real possibility of election reform.  As we weighed the merits of various>methods it suddenly became apparent that we didn't have a Condorcet method that was immune to both burial abd "Chicken,">a ploy that had not concerned us much in the past but now loomed larger.
For my part, the chicken dilemma was always a concern for me when designing methods. It hasweighed on my mind more heavily in recent years, though, I will say.
The problem has always been that there was not, and in my view still IS not, any real solution on thetable. At least if limited to the UD methods. My best idea is that defection without burial just not beallowed, which raises other questions.
For me, Mike's proposed CDC is a complete disaster. It is expensive, it involves mind-reading, itprobably would achieve an outcome other than its intended one, it is barely defined, and its definitionseems to make a sneaky concession to Condorcet methods that strikes me as unwarranted giventhe goal of the criterion. (Namely, one of the two factions is ALLOWED to defect! What??)
So, I was disappointed by this development.

>Now here is a suggestion for a minimal departure from Universal Domain that makes both Burial and Chicken gambits too
>risky to be practical with added benefit of potentially settling the wv versus margins debate once and for all!>
>[But probably not before the debate about round or flat earth:-)]>
>To each ranked preference ballot append a check box labeled "symmetric completion?"
I'd love to know on what basis the voter makes this decision. There is no need to request that hisOWN ballot be symmetrically completed, so it must have something to do with his assessmentof the race.
But I suppose your idea is to introduce so much uncertainty that no one wants to use any insincere strategy. I'm not sure how well that works. It seems pretty clear that this method would have to havemore compromise incentive than WV, and uncertainty about the method's resolution would probablydrive further compromise incentive, as people seek to minimize risk.
Kevin
  
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