[EM] Anti-defection strategy device for IBIFA

[Michael Ossipoff]

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> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20161103/2e664e94/attachment-0003.htm>