[EM] Anti-defection strategy device for IBIFA

[C.Benham]

On 11/4/2016 4:38 AM, Michael Ossipoff wrote:

> You've mentioned that pushover-incentive spoils FBC. But I don't know 
> of a way that failure could happen with this method.

Yes, my earlier generalisation was mistaken. This method both meets FBC 
and is vulnerable to Push-over.

Normally Push-over involves promoting some weak candidate into a 
(virtual) runoff, and not just switching off an unusual "conditional 
approval"
mechanism.

Chris Benham

> You've mentioned that pushover-incentive spoils FBC. But I don't know 
> of a way that failure could happen with this method.
>
> If I top-rate Compromise & Favorite, that couldn't be any worse for 
> Compromise than if I'd not top-rated Favorite...because top-ratings 
> aren't conditional.
>
> FBC and CD--That's a strong combination.
>
> And the addition of that natural conditional feature to Bucklin is 
> briefer & simpler to define than 3-Slot ICT. Probably suitable for a 
> first replacement of Plurality.
>
> With both methods, if you middle-rate Compromise in 3-Slot ICT, or 
> conditionally approve Compromise in Conditional Bucklin, you aren't 
> fully protecting Compromise.
>
> Compromise could lose to Worst because you aren't helping hir get a 
> top-majority in Conditional Bucklin.   ...or because you didn't 
> protect hir from truncation in 3-Slot ICT.
>
> Neither has the amount of protection of a 2nd-rated (or 2nd-ranked) 
> candidate in MMPO largely because neither has wv-strategy. But, of 
> course MMPO would have little chance of acceptance....whereas 
> Conditional Bucklin could be a successful Bucklin proposal, due to the 
> naturalness of the conditional refinement.
>
> Your objection to MMPO is of course a perfectly valid one. If people 
> don't bother to ensure that less-liked candidates have maximum 
> possible pairwise opposition, then Hitler could win because two people 
> support him.
>
> For hauling, a truck has advantages over a car, but there are various 
> special dangers & precautions for driving a truck, as opposed to a car.
>
> It's a trade-off. I admit that the price for FBC, Weak CD, & 
> wv-strategy is high.
>
> By the way, if there's a special "favorite-designation" on the ballot, 
> separate from the ratings, then even a top-rating could be made 
> conditional (upon the conditionally-top candidate having more 
> favorite-designations than your favorite-designated candidatge)
>
> And, with that separate favorite-designation on the ballot, there 
> could be Conditional-Approval.
>
> I notice that there are two e-mail addresses for EM. I'm sending this 
> post to both addresses. If it posts twice, I'll know that they both work.
>
> .Michael Ossipoff
>
>
>
>
> On Thu, Nov 3, 2016 at 8:53 AM, C.Benham <cbenham at adam.com.au 
> <mailto: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
>     <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/Chicken_Dilemma_Criterion>
>
>     http://wiki.electorama.com/wiki/Minimal_Defense_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
>
>
> No virus found in this message.
> Checked by AVG - www.avg.com <http://www.avg.com>
> Version: 2016.0.7859 / Virus Database: 4664/13342 - Release Date: 11/03/16
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20161104/fe820780/attachment-0003.htm>