[EM] Defeat strength, Winning Votes vs. Margins, what to do with equal-ranks on the ballot?

robert bristow-johnson rbj at audioimagination.com
Thu May 23 16:30:51 PDT 2019




 
I think all unranked candidates are tied for last place, no?  Are there any variants of RCV that this is different?
Whether equally-ranked candidates are counted as votes for *both* candidates or for *neither* candidates cannot make a difference for Margins.  But it
seems to me that it makes a difference if Winning Votes is the measure of defeat strength.
regrads,
r b-j



---------------------------- Original Message ----------------------------

Subject: Re: [EM] Defeat strength, Winning Votes vs. Margins, what to do with equal-ranks on the ballot?

From: Stéphane Rouillon <stephane.rouillon at sympatico.ca>

Date: Thu, May 23, 2019 4:24 pm

To: rbj at audioimagination.com

Cc: election-methods at lists.electorama.com

--------------------------------------------------------------------------



> All criterias (Winning Votes, Margins, Relative Margins) have advantages and are acceptable. The fine choice depends on the interpretation you told voters that would be made of blank ballots. If a blank rank means "all bad", WV is perfect. If it means "all the same" Margin
is good, and if it means "I don't know but I trust other voters to express a valid opinion about this option", then RM is perfect. Just tell voters the chosen interpretation of blank tanks in advance so they can fill a sincere ballot...
>

> Envoyé de mon iPhone

>

>> Le 22 mai 2019 à 20:18, robert bristow-johnson <rbj at audioimagination.com> a écrit :

>>

>>

>> i'm posting this to the list. i hope it's okay.

>>

>> i had been asked:

>>

>> > This "plausible example" you can think of, why don't you show it to us?

>>

>> i'm not as good as you guys in dreaming up the number of ballots ranked however:

>>

>> ex. A>B>C>D

>>

>> but could you have a defeat matrix where

>>

>> A>B>C

>>

>> but C>A by a smaller defeat strength than A>B or B>C. But D>A by an even smaller defeat strength, however D<B and D>C?

>>

>> i dunno how to dream up ballot combinations to do that.

>>

>>

>> > Without it all I can say that is that the River winner may or may not be

>> > a "better choice" than the

>> > RP winner.

>> >

>> > River's main practical point is that it easier than Schulze and RP to use.

>>

>> i think it's more complicated than RP. it's RP with an additional exception.

>>

>>

>>

>> i have to say i am still not convinced of WV. probably Schulze-Margins is still the best, but RP-Margins good enough and possibly easier to sell to policy makers and the public.

>>

>> i like Margins in principle: The percentage Margin is (WV-LV)/(WV+LV) and is a measure of the decisiveness of defeat, without respect to the size of the election. So 5% defeat is a more decisive defeat than a 4% defeat.

>>

>> But if you consider every Condorcet pair as it's own little election, then the salience of the election would be the number of voters that weigh in on it, which is WV+LV.

>>

>> So if the net defeat strength (the index to rank the pairs) is the product of how important the election is with the decisiveness of defeat you get:

>>

>> (WV+LV) x (WV-LV)/(WV+LV) = WV - LV

>>

>> it just seems to me that Margins is better than WV.

>>

>> but say, WV, is a good idea for defeat strength. is LV a better idea?

>>

>> hmmmm.

>>

>> --

>>

>> r b-j rbj at audioimagination.com

>>

>> "Imagination is more important than knowledge."

>>

>>

>>

>>

>>

>>

>>

>>

>> ----

>> Election-Methods mailing list - see https://electorama.com/em for list info

>
 
 
 


--



r b-j                         rbj at audioimagination.com



"Imagination is more important than knowledge."

 
 
 
 
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