[EM] IRV variants

[Chris Benham]

Forest,

"....the IRV- Condorcet you 
describe here is a simpler solution, as long as you allow equal rankings, and count them as whole (as 
opposed to fractional):"
 
I am strongly opposed to allowing  equal ranking (except for truncation) in IRV or  IRV-like Condorcet
methods.  As I've explained more than once on EM, that just makes Push-over strategising much easier.
 
And in this respect the "whole vote" version is much worse than the "fractional" version. If you are confident
that your favourite will make the final runoff and that your favourite will have a pairwise win versus some
turkey with you being merely neutral (not supporting the turkey as you'd have to do in regular IRV) then
you should vote the turkey equal-top with your favourite.
 
You are still giving a whole vote to help your favourite make the top 2, so on the whole the strategy is 
much less risky and easier to carry out than with regular IRV and  to a lesser extent the Fractional version.
 
Chris


________________________________
From: "fsimmons at pcc.edu" <fsimmons at pcc.edu>
To: C.Benham <cbenhamau at yahoo.com.au>
Cc: em <election-methods at electorama.com>
Sent: Thursday, 10 November 2011 5:54 AM
Subject: Re: IRV variants

> I don't get it. (I am confused by your explanation of the 
> algorithm).
> How do you think this is better than your latest version of 
> Enhanced DMC?

It takes care of the chicken problem.  But forget my confusing process; the IRV- Condorcet you 
describe here is a simpler solution, as long as you allow equal rankings, and count them as whole (as 
opposed to fractional):

> 
> I think a good method is the IRV-Condorcet hybrid that differs 
> from IRV 
> only by before any and each elimination
> checks for an uneliminated candidate X that pairwise beats all 
> the other 
> uneliminated candidates and elects the
> first such X to appear.

Yes this is simpler.

> 
> That of course gains Condorcet, and it keeps IRV's Mutual 
> Dominant Third 
> Burial Resistance property.
> So if a candidate X pairwise beats all the other candidates and 
> is 
> ranked above all the other candidates on more than
> a third of the ballots then (as with IRV) X must win and a rival 
> candidate Y's supporters can't get Y elected (assuming
> they can somehow change their ballots) by Burying X.
> 
> Does your method share that property?
> 
> > 49 C
> > 27 A>B
> > 24 B
> >
> > Candidate A starts out as underdog, survives B, and is beaten 
> by C, so 
> > C wins.
> 
> 
> From what I think I do understand of your algorithm 
> description, 
> doesn't candidate B start out as "underdog"?

Yes, I was in too much of a hurry when I wrote that.

Also contrary to my hopes the method turned out to be non-monotonic, because the IRV elimination 
order can eliminate a candidate earlier as a result of more first place support.  Only elimination orders 
without this defect can be used as a basis for a monotone method.

Forest
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