<div dir="ltr"><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Michael Ossipoff</b> <span dir="ltr"><<a href="mailto:email9648742@gmail.com">email9648742@gmail.com</a>></span><br>Date: Thu, Nov 3, 2016 at 1:25 PM<br>Subject: Re: Anti-defection strategy device for IBIFA<br>To: "C.Benham" <<a href="mailto:cbenham@adam.com.au">cbenham@adam.com.au</a>><br><br><br><div dir="ltr"><div><div><div>Well I guess it wouldn't work with Approval. The separate top-rating is necessary. <br><br></div>But surely it would with ordinary Bucklin. <br><br></div>No doubt your improved interpretation of "majority" is an improvement, but it complicates the definition too much for a first replacement of Plurality.<span class="HOEnZb"><font color="#888888"><br><br></font></span></div><span class="HOEnZb"><font color="#888888">Michael Ossipoff<br></font></span><div><div><div><div><div><div class="gmail_extra"><br><div class="gmail_quote"><span class="">On Thu, Nov 3, 2016 at 8:53 AM, C.Benham <span dir="ltr"><<a href="mailto:cbenham@adam.com.au" target="_blank">cbenham@adam.com.au</a>></span> wrote:<br></span><div><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I normally don't like explicit strategy devices, and (beyond considering it desirable to elect from the<br>
voted Smith set) don't care very much about the "center squeeze" effect.<br>
<br>
(I like truncation resistance, so I'm happy with some of the methods that meet the Chicken Dilemma criterion.)<br>
<br>
Nonetheless here is version of IBIFA with a device aimed at addressing the Chicken Dilemma scenario.<br>
<br>
* Voters mark each candidate as one of Top-Rated, Approved, Conditionally Approved, Bottom-Rated. Default is Bottom-Rated.<br>
<br>
A candidate marked "Conditionally Approved" on a ballot is approved if hir Top Ratings score is higher than the highest<br>
Top Ratings score of any candidate that is Top-Rated on that ballot.<br>
<br>
Based on the thus modified ballots, elect the 3-slot IBIFA winner.*<br>
<br>
("Top-Rated" could be called 'Most Preferred' and "Bottom-Rated" could be called 'Unapproved' or 'Rejected').<br>
<br>
To refresh memories, IBIFA stands for "Irrelevant-Ballot Independent Fall-back Approval", and the 3-slot version goes thus:<br>
<br>
*Voters rate candidates as one of Top, Middle or Bottom. Default is Bottom. Top and Middle is interpreted as approval.<br>
<br>
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<br>
with the highest Top-Ratings score wins.<br>
<br>
Otherwise the most approved candidate wins.*<br>
<br>
<a href="http://wiki.electorama.com/wiki/IBIFA" rel="noreferrer" target="_blank">http://wiki.electorama.com/wik<wbr>i/IBIFA</a><br>
<br>
35: C<br>
33: A>B<br>
32: B (sincere might be B>A)<br>
<br>
In the scenario addressed by the Chicken Dilemma criterion, if all (and sometimes less than all) of A's supporters only "conditionally"<br>
approve B then the method meets the CD criterion. Otherwise it meets the Minimal Defense criterion.<br>
<br>
<a href="http://wiki.electorama.com/wiki/Chicken_Dilemma_Criterion" rel="noreferrer" target="_blank">http://wiki.electorama.com/wik<wbr>i/Chicken_Dilemma_Criterion</a><br>
<br>
<a href="http://wiki.electorama.com/wiki/Minimal_Defense_criterion" rel="noreferrer" target="_blank">http://wiki.electorama.com/wik<wbr>i/Minimal_Defense_criterion</a><br>
<br>
Of course it meets the Plurality criterion and doesn't have any random-fill incentive.<br>
<br>
The downside is that the use of Conditional Approval can cause a vulnerability to Push-over strategy.<br>
<br>
48: C<br>
27: B<br>
25: A>>B<br>
<br>
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<br>
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<br>
and then C wins.<br>
<br>
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<br>
they were foolish not to conditionally approve A. If they'd done that then the attempted Push-over would have just elected A.<br>
<br>
(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<br>
or Benham that allows above-bottom equal-ranking, but that would have broken compliance with FBC.)<br>
<br>
Chris Benham<br>
<br>
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