[EM] Simple Acceptable Ranked Choice Voting

[Forest Simmons]

The candidate added to the tail would be the one defeated most strongly by
the current tail. Whether to lengthen the chain forward or backwards at a
given stage would depend on which new direct defeat was stronger.

On Sat, Jan 7, 2023, 5:05 PM Kevin Venzke <stepjak at yahoo.fr> wrote:

> Hi Forest, I may give it a look, but a couple of issues.
>
> One thing, I feel a little unsure it will be monotone to pick a new
> candidate to add to the
> chain based on who the current head is. Normally these methods don't
> actually depend on the
> ordering of candidates already in the chain.
>
> > It is well known that not all nice properties are compatible with each
> other in a common
> > single winner voting method. However, we shall see by example that the
> following nice
> > features are mutually compatible in a simple RCV voting method (MGCB
> defined below).
> > Therefore, excluding any of them can only be justified by trading in the
> excluded ones for
> > equally important ones in an equally simple method.
> >
> > 1. The method should be clone independent like IRV ... therefore not
> plagued by the spoiler
> > problem like First Past The Post Plurality or by "teaming" like the
> Borda Count.
>
> Generous of you to imply that IRV is not plagued by a spoiler problem.
>
> > It was a comment of Kristofer that inspired this method. He mentioned
> that according to his
> > recent simulations electing the winner of the over-all strongest defeat
> A>B is a
> > surprisingly burial resistant stand-alone method.  It seems to me that
> the burial resistance
> > should carry over to this MGCB completion of his discovery.
>
> Well. That kind of method is a stone's throw away from just being approval.
>
> > Furthermore, it appears that if defeat strength is gauged by margins,
> then the method is
> > Chicken resistant.
>
> If you mean "more" chicken-resistant then OK, but if you mean satisfying
> the CD criterion,
> there's no reason for that to be true. If you want to guarantee CD you
> need to deliberately
> reject some majorities (which is completely in its spirit), not simply be
> indifferent to
> them.
>
> More importantly, I would point out that from a CD criterion standpoint,
> the Alaska RCV
> outcome was probably completely correct.
>
> It seems to me the Alaska race demonstrates that the CD criterion can't
> deliver on its
> promise even under IRV, its most advantageous setting. It's not going to
> be better under a
> method that poses actual incentives to withhold lower preferences.
>
> > A fairly simple modification ... where the chain is built up from both
> ends ... always
> > giving priority to the end where the new defeat is stronger ....
> preserves all six of the
> > nice features in our list while adding a Strong Reverse Symmetry feature
> ... reversing all
> > of the ballot rankings precisely reverses the output chain .... swapping
> the head and tail
> > of the completed chain.
>
> I don't follow. Are you just saying there's a choice of whether you beat
> the head or the
> tail, but in either case the newly added candidate becomes the new head?
>
> Kevin
> votingmethods.net
>
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