[EM] Holy grail: PAR with FBC?

[Jameson Quinn]

Kevin Venzke is right: the method I'd called PARFBC does not actually meet
FBC. However, it is bloody close; I'm trying to define an FBC-like
guarantee that it does meet.

I think it's better, and closer to FBC, than Kevin's prior version without
step 2, because in a chicken dilemma case, the winner actually gets more
votes in step 4. Because in my version, the mutual threat candidate C is
eliminated before it ever becomes the leader, so most-preferred wins,
without causing a slippery slope by showing all accepted votes and thus
having least-rejected win.

2016-11-07 20:25 GMT-05:00 Kevin Venzke <stepjak at yahoo.fr>:

> Hi Jameson,
>
> Except for a couple of details I have a method like this on the wiki
> (called CdlA). The differences are that I don't have step 2 at all, and in
> step 4 instead of "don't prefer the leader" I have "reject the leader."
>
> Under my method, FBC is violated because if my favorite happens to become
> a tally leader, this could cause other voters, who reject my favorite, to
> provide additional preferences that I may not myself like. (Whereas, if I
> had not top-rated my favorite, the other voters' preferences may have
> stayed concealed.) Generally speaking we have to guarantee that raising a
> favorite to equal-top won't change the winner unless it makes the favorite
> win. Alternatives are possible, but we would have to be extremely careful
> in how we use the information.
>
> I believe under your method, the only time a voter doesn't eventually
> upgrade his "accepts" into "prefers" is if he prefers every tally leader
> that ever comes up. I guess most of the time, accepts and prefers end up
> counting the same. But the concern would be that there are ballots out
> there that prefer all the tally leaders (including my compromise choice,
> but excluding my favorite) and accept some candidates worse than my
> compromise. In that case I could regret voting for my favorite because of
> how it affects the influence contributed by other voters.
>
> I tend to appreciate methods along these lines, though, because they
> emulate, to some extent, a realistic process of group decision making.
>
> Kevin
>
>
> ------------------------------
> *De :* Jameson Quinn <jameson.quinn at gmail.com>
> *À :* electionsciencefoundation <electionscience at googlegroups.com>; EM <
> election-methods at lists.electorama.com>
> *Envoyé le :* Lundi 7 novembre 2016 8h27
> *Objet :* [EM] Holy grail: PAR with FBC?
>
> Here's a new system. It's like PAR, but meets FBC, and deals with center
> squeeze correctly in the few tricky cases where PAR doesn't. I'm
> considering using the PAR name for this system, and renaming the current
> PAR to something like "Old Par
> <http://sr3.wine-searcher.net/images/labels/29/06/grand-old-parr-12-year-old-blended-scotch-whisky-scotland-10152906t.jpg>".
> Meanwhile, the system below is temporarily called PARFBC
> <http://wiki.electorama.com/wiki/PARFBC_voting>.
>
>
>    1. Voters can Prefer, Accept, or Reject each candidate. Default is
>    Accept.
>    2. Candidates with a majority of Reject, or with under 25% Prefer, are
>    eliminated, unless that would eliminate all candidates.
>    3. Tally "prefer" ratings for all non-eliminated candidates.
>    4. Find the leader in this tally, and add in "accept" ratings on
>    ballots that don't prefer the leader (if they haven't already been tallied).
>    5. Repeat step 4 until the leader doesn't change. The winner is the
>    final leader.
>
>
> ...
>
> This is pretty much a holy grail system from my perspective. It meets FBC
> (I think; I don't have a proof, but it seems to me it should). It deals
> with a simple chicken dilemma without a slippery slope. It deals with
> center squeeze with naive ballots. I think it even meets the voted majority
> Condorcet criterion, in an election with 3 candidates and where all ballots
> use the full range (and you can add irrelevant "also-rans" to such an
> election without breaking any compliances).
>
> It has a sequential counting process like IRV, and so it fails
> summability; but in most cases, step 4 will not change the outcome, so will
> happen only once. (The main exception is if there's a voted Condorcet
> cycle.)
>
> It even meets weakened versions of both Later No Help and Later No Harm;
> weak enough so that they are compatible with the above passed criteria, but
> strong enough so that I think most voters would be honest. Later No Help
> holds if there's no possible Condorcet cycle; and Later No Harm holds if
> the "later" candidate isn't on the edge of being eliminated.
>
> I think that the explanation is clear and intuitive enough to be
> reasonably acceptable to most voters. It involves only simple adding to
> tallies, not anything couched in terms of sets or multiplication or the
> like.
>
> Does anybody have any reason why this system should not be considered a
> leading contender for "next step after approval"?
>
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