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