[EM] Score Voting and Approval Voting not practically substantially different from Plurality?

[Kristofer Munsterhjelm]

On 06/25/2013 09:00 AM, Juho Laatu wrote:
> On 25.6.2013, at 1.06, Kristofer Munsterhjelm wrote:
>
>> Remember that criterion compliances are absolute. So a method may
>> fail a criterion yet be perfectly acceptable in real elections.
>
> I just want to support this viewpoint. It is not essential how many
> criteria a mehod violates. It is more important how bad those
> violations are, i.e. if the method likely have serious problems or
> not. The best method might well be a method that violates multiple
> criteria, but manages to spread the  (unavoidable) problems evenly so
> that all of them stay insignificant.

In a sense, it's like certain kinds of mathematical tests. There are 
primality tests that return either "this number is definitely a prime" 
or "this number might be prime or might be composite". If you get the 
former result, you know you're dealing with a prime, but if you get the 
second, you don't know whether you're dealing with a prime or a 
composite number.

Criterion compliances are similar. If something passes IIA, you don't 
have to worry about candidates being added or removed as long as the 
voters don't alter their votes when the candidates are being 
added/removed. Whatever the dynamics might be on the nomination side, 
IIA secures the method. On the other hand, if something fails IIA, then 
you have the "might be" scenario. The method might fail IIA in blatant 
ways, or it might fail it where it doesn't really matter. You don't know.

In my case, I do like the certainty that criterion compliance provides, 
but sometimes, it just isn't available.

There is, though, one situation where criterion compliances go both 
ways. The method might produce a result that goes so completely against 
common sense that opponents can use it to argue against the method, even 
if that result itself only would appear very rarely. Perception does 
matter; and it's reasonable that it does, because sometimes the bizarre 
failure is symptomatic of a method that behaves strangely under pressure 
in general. That is not true all the time, though.