[EM] A possible solution to SNTV vote-splitting

[Raph Frank]

On Wed, Feb 10, 2010 at 7:33 AM, Kristofer Munsterhjelm
<km-elmet at broadpark.no> wrote:
> It is according to the (original, unmodified) cumulative ballot, so that the
> method passes Majority in the single-winner case.
>
> I suppose you could have this as a parameter: if the parameter is on, it
> uses rescaled ballots - if not, it treats them as Range.

It is unclear what is the best way to handle this.  You could have a
rule that if a group of voters can get a better result by dissenting,
and not being part of the "change" group then they should dissent.
However, that becomes infinite regress.

>> Anyway, his idea is to use borda to decide elimination ordering.
>
> I think I've heard of that, and I actually implemented it in my simulator.
> It works, but the results suffer. I haven't checked if it's more monotone
> than ordinary STV, though.
>
> Instead of Borda, you could use any elimination order (for instance, by some
> Condorcet method), as well. That would be an easy way to reduce the
> single-winner instance to your favorite Condorcet method: all candidates but
> your winner ends up eliminated.

The problem with using a condorcet method (and probably Borda too) is
that it is unfair to some factions (mostly extreme factions).
Effectively, other people choose their elimination ordering.  Although
PR, it would elect the candidate from each faction closest to the
centre of all the voters.  This would encourage strategic voting by
extreme factions so as not to give that option.  A candidate with 90%
of the factions vote could end up being eliminated before a second
candidate from the faction, if the electorate as a whole prefers the
2nd candidate.

PR-STV effectively uses IRV for the intra faction elections.

Another possible method would be to use approval, but require that it
is consistent with the rankings.  Every candidate above the cutoff is
approved.  A voter would then have to give up their ability to
determine the election ordering in their faction in order to affect
the election ordering in another faction.