[EM] A method "DNA" generator, tester, and fixer

[Kevin Venzke]

Hi Juho,

--- En date de : Mer 26.5.10, Juho <juho4880 at yahoo.co.uk> a écrit :
> >>>> The following criterion is similar to
> >> Plurality.  Does
> >>>> it have a name?
> >>>> 
> >>>> If the number of ballots on which X beats
> Y is
> >> greater than
> >>>> the number of
> >>>> ballots on which Y is ranked, then Y
> cannot be
> >> elected.
> >> 
> >>>> Any decent method that doesn't satisfy
> it?
> >>> 
> >>> This criterion is strictly stronger than
> Plurality, so
> >> I'd have to ask
> >>> whether you think any decent methods fail
> Plurality.
> >> Probably the answer
> >>> is no, not really.
> >> 
> >> This says that all typical margins based Condorcet
> methods
> >> would not be "decent". One could ask the question
> also in
> >> the reverse direction. All methods violate some
> criteria
> >> that look good at least at first sight. Which
> property of
> >> the plurality criterion (or the new criterion)
> makes it a
> >> mandatory requirement for all election methods (or
> Condorcet
> >> or ranked methods)?
> > 
> > Personally I would allow Plurality failures for a good
> reason.
> > 
> > But I think that most people would generally not be
> accepting. This would
> > be because of a view that there is such a thing as
> "support" involved in
> > voting for a candidate and this can't be found when
> one truncates a
> > candidate. So when you compare a candidate X who is
> the favorite of 10
> > voters, and you can't find that many voters who
> "support" Y on their
> > ballots in any way, something seems wrong when Y wins.
> The thought is
> > why would you ever need to elect Y when you could just
> elect X? It's
> > similar to Pareto in that sense.
> 
> Yes, in ballots where the position of truncated (or shared
> last) candidates looks clearly different than the position
> of other candidates the voters may get the impression that
> thy are supporting all others and not supporting the
> truncated / shared last candidates. And they may vote this
> way and dislike methods that do do not respect their
> impression on what should happen with respect to candidates
> with lots of first preferences vs. candidates with less any
> higher than last preferences. But on the other hand all
> methods need not have such implicit approval/support
> assumptions.

Well, you can argue with voters or you can argue with me. I personally
don't see value in what margins wants to substitute, so I don't see
that margins has a good reason for failing Plurality.

> It depends also a lot on the environment if one should
> optimize the method so that it will perform well under all
> (sincere and/or strategic) circumstances or if it should
> look good to the average voters and politicians so that it
> will have a chance of getting adopted. If one wants e.g. to
> promote Condorcet methods one could (in theory) listen to
> the discussion for a while and then pick a method that looks
> best in the observed discussion environment (the behaviour
> of all Condoret methods is anyway quite similar in typical
> elections).

They are similar but whether the different incentives are significant
can't easily be proven.

> There could be also other criteria that people want to see
> implemented. They might for example hate "favourite
> betrayal", and that could make all Condorcet methods
> unusable. If people study election methods in detail they
> must accept that all the best election methods will violate
> some nice looking criteria.

Yes. If I thought that Forest thought failing FBC was unacceptable then
when I guess whether an FBC-failing method is decent to him, I would
say probably not. If he thinks Mono-add-top is crucial and Plurality is
not then I guess margins is a decent method for him.

> Btw, in the example above I guess the plurality criterion
> doesn't requite that X should win. Also some other candidate
> with sufficient number of above last rankings could win. In
> that sense methods that meet the plurality criterion might
> not be an exact match to the needs of that voter who wanted
> X to win with 10 votes.

There is no voter who wanted X to win. The issue is that it is cut and
dry that X is better than Y; Z may be better than either but we may not
be able to easily show it. It's no different from Pareto there.

Kevin