[EM] SFC

[Chris Benham]

Warren Smith wrote:

>>"SFC: If no one falsifies a preference, and there's a CW, and a 
>>majority of all the voters
>>prefer the CW to candidate Y, and vote sincerely, then Y shouldn't win."
>>    
>>
>
>I must say, SFC is then rather silly.         
>It says "if no one falsifies a preference" redundantly since it also says
>"a majority of all the voters prefer the CW to candidate Y"
>(of course they do, that followed  from defn of CW and fact nobody falsified a preference)
>and redundanty it also says "and vote sincerely" (of course they do, since
>nobody falsified a preference)
>
The criterion refers to all sincere preferences, and by "falsifies" it 
means order-reverse and not just truncate or
otherwise falsely equal-rank. It is about a faction whose favourite Y 
isn't the sincere CW not being able to elect Y
just by truncating.

So say sincere is

43: A>B
10: B>A
10: B>C
37: C>B

B is the CW, so "there's a CW".  If  the A supporters truncate

43: A
10: B>A
10: B>C
37: C>B

Now  C>B>A>C,  but  no-one has "falsified" a preference and more than 
half the voters ("a majority")
have "voted sincerely" expressing their preference for the (sincere) 
"CW"(B) over "Y" (A in this example,
B>A 57-43),  so the criterion says that in this scenario A mustn't win.

This isn't the same as the Condorcet criterion, because  
BP/RP/MM/River(Margins) and Smith/Schwartz,IRV
all meet Condorcet but elect A.

I speculate that the reason for the confusing unusual language is to do 
with Mike's long-running propaganda
war in favour of  Winning Votes and Approval  versus Margins and IRV.

My stab at making it clearer and more "technical":

"If  more than half the voters vote X over Y and it is possible to 
complete truncated ballots in a way to
make X the CW, then Y must not win."


Chris Benham




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