[EM] Fwd: Anti-defection strategy device for IBIFA

[Michael Ossipoff]

---------- Forwarded message ----------
From: Michael Ossipoff <email9648742 at gmail.com>
Date: Thu, Nov 3, 2016 at 1:25 PM
Subject: Re: Anti-defection strategy device for IBIFA
To: "C.Benham" <cbenham at adam.com.au>


Well I guess it wouldn't work with Approval. The separate top-rating is
necessary.

But surely it would with ordinary Bucklin.

No doubt your improved interpretation of "majority" is an improvement, but
it complicates the definition too much for a first replacement of Plurality.

Michael Ossipoff

On Thu, Nov 3, 2016 at 8:53 AM, C.Benham <cbenham at adam.com.au> wrote:

> I normally don't like explicit strategy devices, and (beyond considering
> it desirable to elect from the
> voted Smith set) don't care very much about the "center squeeze" effect.
>
> (I like truncation resistance, so I'm happy with some of the methods that
> meet the Chicken Dilemma criterion.)
>
> Nonetheless here is  version of  IBIFA with a device aimed at addressing
> the Chicken Dilemma scenario.
>
> * Voters mark each candidate as one of  Top-Rated, Approved, Conditionally
> Approved, Bottom-Rated. Default is Bottom-Rated.
>
> A candidate marked "Conditionally Approved" on a ballot is approved if hir
> Top Ratings score is higher than the highest
> Top Ratings score of any candidate that is Top-Rated on that ballot.
>
> Based on the thus modified ballots, elect the 3-slot IBIFA winner.*
>
> ("Top-Rated"  could be called 'Most Preferred' and "Bottom-Rated" could be
> called 'Unapproved' or 'Rejected').
>
> To refresh memories, IBIFA stands for "Irrelevant-Ballot Independent
> Fall-back Approval", and the 3-slot version goes thus:
>
> *Voters rate candidates as one of  Top, Middle or Bottom. Default is
> Bottom.  Top and Middle is interpreted as approval.
>
> If any candidate X  is rated Top on more ballots than any non-X is
> approved on ballots that don't top-rate X, then the X
> with the highest Top-Ratings score wins.
>
> Otherwise the most approved candidate wins.*
>
> http://wiki.electorama.com/wiki/IBIFA
>
> 35: C
> 33: A>B
> 32: B (sincere might be B>A)
>
> In the scenario addressed by the Chicken Dilemma criterion, if all  (and
> sometimes less than all) of A's supporters only "conditionally"
> approve B then the method meets the CD criterion.  Otherwise it meets the
> Minimal Defense criterion.
>
> http://wiki.electorama.com/wiki/Chicken_Dilemma_Criterion
>
> http://wiki.electorama.com/wiki/Minimal_Defense_criterion
>
> Of course it meets the Plurality criterion and doesn't have any
> random-fill incentive.
>
> The downside is that the use of  Conditional Approval can cause a
> vulnerability to Push-over strategy.
>
> 48: C
> 27: B
> 25: A>>B
>
> The A supporters are all only conditionally approving B, but that has the
> same effect as normal approval because B has a higher Top Ratings score
> than A.  But now if 3 to 22 of the C voters change to C=A  then A's  Top
> Ratings score rises above B's so the "conditional" approval is switched off
> and then C wins.
>
> I dislike this "at the same time"-no-help failure, but the new result
> doesn't look terrible and of course if the B voters really prefer A to C
> then
> they were foolish not to conditionally approve A. If they'd done that then
> the attempted Push-over would have just elected A.
>
> (It crossed my mind to try to make Push-over strategising  more difficult
> and riskier with the same mechanism I suggested a while ago for IRV
> or Benham that allows above-bottom equal-ranking, but that would have
> broken compliance with FBC.)
>
> Chris Benham
>
>
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