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

[Kevin Venzke]

Hi Robert,

A few comments on this exchange...


>> Another Condorcet-compliant method that might interest you, from a Kevin
>> Venzke webpage:
>>
>>> *Jobst Heitzig's River method* is identical to Tideman's method,
>>> except that one additionally ignores (without locking) defeats against
>>> candidates against whom some defeat has already been locked. This is
>>> possibly the easiest of the three to work out by hand.
>maybe someone needs to explain this more to me.  i can think of a plausible example where it may differ from 
>RP, but i can't think of what the motivating principle is.  if River and RP disagree, why is the River winner a better choice?

There are theoretical arguments for each method, but for me the appeal of River is not that it gives a 
better winner but that it's easier to find the result. You don't have to look at as many pairwise contests
as with RP.

>> The other two he is referring to are Schulze and Tideman RP. Nearly all
>> the time it will elect the same candidate and as far as I know is at
>> least as good.
>well, we know when there are only 3 in the Smith Set, that Schulze and Tideman pick the same winner.  
>dunno about this River method, though.

Yes, it's the same.

>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 really wonder. Could you sell A winning the below election? Especially to someone who doesn't know
about pairwise matrices. The IRV or Bucklin advocate will find this absurd I would guess.

7 A>B.
5 B.
8 C.

>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.

I feel the loser of the most "salient" election should not be elected. I think this is in the same vein as
saying that elections shouldn't be vulnerable to spoilers. E.g. if less salient contests affect the outcome 
it's likely they do so without benefit to the winners of those contests. (As there is only one prize to give
out.)

Kevin