[EM] Juho--Margins fails Plurality. WV passes.

[Michael Ossipoff]

I'd said:

>>But if we're going to have the added definition-wordiness of  Condorcet, 
>>we should get what Condorcet can offer, including  compliance with the 
>>Plurality Criterion, SFC, GSFC, and SDSC, and  URNEC.
>

Juho replied:

>And maybe [will you provide]  pointers to the definitions of these too.

I reply:

Sure, I will. But for right now, I've defined URNEC recenly in an EM  
posting addressed to you.

And I and others posted SFC's definition to EM almost as recently, when a 
few people were looking for faults in it.

But let me start by re-stating URNEC here:

A method passes URNEC if, for all situations (configurations of candidates, 
voters, and voters' preferences) when there is a CW, there is always a Nash 
equilibrium in which the CW wins and no one reverses a preference.

[end of URNEC definition]

Approval, Condorcet(wv) and MDDA pass URNEC. Margins, IRV, and Plurality 
fail URNEC.

I may not have recently posted SDSC's defilniltion here, so let me do so 
now:

Strong Defensive Strategy Criterion (SDSC):

If a majority prefer X to Y, the they should have a way of voting that 
ensures that Y won't win,without any member(s) of that majority voting a 
candidate that they like less equal to or over a candidate that they like 
more.

One votes X equal to Y if one votes X over someone, and votes Y over 
someone, but doesn't vote X over Y and doesn't vote Y over X.

[end of SDSC defilnition]

So voting X equal to Y only refers to X and Y that the voter considers good 
enough to rank. If the voter doesn't vote for X and doesn't vote for Y, s/he 
isn't voting X equal to Y, as the term is used in the above definiltion. 
That makes sense, because the candidates who are good enough to rank are the 
ones that you don't want to demean by votng someone less-liked equal to 
them.

I'll re-post SFC and is supporting definitioins tomorrow. I'd do it now, but 
there are, as I said, a few supporting definitions, and I've been on the 
computer for a long time tonight.

Mike Ossipoff




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