[EM] Fwd: Fwd: U/P voting: new name for simple 3-level method.
C.Benham
cbenham at adam.com.au
Tue Sep 13 03:28:20 PDT 2016
Kevin,
I take "downvoted by most" to mean down-voted by most of the voters,
meaning down-voted on more than half the ballots.
Your interpretation would be "the most downvoted".
Chris Benham
On 9/13/2016 2:56 PM, Kevin Venzke wrote:
> Hi Jameson,
>
> "Downvoted by most" means the candidate with the single greatest
> number of downvotes? This could be the (voted, unique) majority
> favorite couldn't it?
>
> How does this violate "irrelevant ballots"? I must be misunderstanding
> it. Does "max amount of upvotes" mean 100% of the voters, or just the
> greatest number of upvotes that occurs?
>
> I do like antiplurality mechanisms.
>
> Kevin
>
>
> ------------------------------------------------------------------------
> *De :* Jameson Quinn <jameson.quinn at gmail.com>
> *À :* Kevin Venzke <stepjak at yahoo.fr>; electionsciencefoundation
> <electionscience at googlegroups.com>
> *Cc :* EM <election-methods at lists.electorama.com>
> *Envoyé le :* Lundi 12 septembre 2016 20h37
> *Objet :* Re: [EM] Fwd: Fwd: U/P voting: new name for simple 3-level
> method.
>
> Here's a new proposed variant of U/P with a simple default:
>
> Voters may rate each candidate as "unacceptable" (downvote),
> "preferred" (upvote), or "acceptable" (neither). Default is neither.
>
> Any candidate downvoted by most, or with fewer than half the max
> amount of upvotes, is disqualified, unless that would disqualify
> everyone. The winner is the remaining candidate with the most upvotes.
>
> The "fewer than half the max" rule prevents dark-horse winners,
> without resorting to strange defaults. It has no effect on a two-way
> chicken dilemma. Though in theory it could affect an evenly-balanced
> three-way chicken dilemma (in a four-way race), I think there's a
> negligible chance that such a scenario would be so balanced.
>
> I know that Chris doesn't like this method's violation of "irrelevant
> ballots". Myself, I think that no voters are irrelevant; even if they
> don't express an opinion between the two frontrunners, they may have
> one. (True, they may not; but that's not the first assumption I'd make.)
>
> 2016-09-12 20:22 GMT-04:00 Kevin Venzke <stepjak at yahoo.fr
> <mailto:stepjak at yahoo.fr>>:
>
> Hi Jameson,
>
> I think it is a positive thing that the MTA B/C majority coalition
> can give their sincere preferences (!), while using the strategy
> they're expected to use (i.e. middle slot as tiebreaker given
> multiple majorities), without risk of this strategy backfiring.
> (Voters can accidentally elect the less preferred of B or C, but
> that is the inescapable chicken dilemma, I would say.)
>
> I have some sympathy for your claim that C should not be able to
> win with few top ratings. But that sympathy is not tied to Borda
> counts, it is based on wanting to reduce the truncation incentive
> for the B voters. This, U/P does not really do, because the B>C
> voters would be taking a large risk that they are helping to put C
> (alone) over the threshold of majority approval.
>
> So I don't think either of these ballot sets is likely under U/P,
> and it sounds like you agree with that and think it is good
> (because it deters a pathological ballot set)? Do you have a
> stance (or at least, see use in determining a stance) on how U/P
> voters in these scenarios should be voting?
>
> Kevin
>
>
> ------------------------------------------------------------------------
> *De :* Jameson Quinn <jameson.quinn at gmail.com
> <mailto:jameson.quinn at gmail.com>>
> *À :* EM <election-methods at lists. electorama.com
> <mailto:election-methods at lists.electorama.com>>
> *Envoyé le :* Dimanche 11 septembre 2016 1h51
> *Objet :* [EM] Fwd: Fwd: U/P voting: new name for simple 3-level
> method.
>
>
>
> 2016-09-10 21:26 GMT-04:00 C.Benham <cbenham at adam.com.au
> <mailto:cbenham at adam.com.au>>:
>
> On 9/11/2016 5:02 AM, Kevin Venzke wrote:
>
> 43: A
> 24: B>C
> 23: C>B
> 10: D
>
> Under MTA the B and C voters are being completely
> reasonable: They hope for majority approval but can still
> hope for a win if they
> don't get it.
>
> Strategy is less likely to produce these ballots under U/P
> because the B and C voters are taking a gamble. To get a
> similar outcome
> they have to vote B=C. Anyone who doesn't is functionally
> defecting!
>
>
> C: A very good example! Assuming MTA and MCA use Top Ratings
> scores to break Approval ties, they both elect the Condorcet
> winner B.
>
>
> But both could be shifted to C with a single C-only ballot, even
> if the B:C ratio were 46:1 instead of 24:23.
>
>
> U/P's under-use of the middle ratings slot means that it
> relies more on its "majority disqualification" mechanism which
> seems to make it more
> vulnerable to irrelevant ballots, as in the example.
>
> Under U/P, without the irrelevant D ballots, A and D are
> disqualified and B is the glorious winner. With them, B and C
> and D are disqualified and (without needing
> any others to be disqualified) A wins.
>
> This causes me to reject U/P as clearly worse than MTA and
> MCA. Of the three I (again) rate MTA as the least bad.
>
>
> I think MTA is pretty darn good. I still prefer U/P.
>
> I think that scenarios like the above are fundamentally
> pathological; any possible winner has only minority approval, so
> that even assuming all ballots are semi-honest, any of them could
> be a true Condorcet loser. Thus, I believe that it's more
> important for a system to try to avoid scenarios like the above,
> than to try to find a perfect winner in such a scenario. In fact,
> in the related scenario:
>
>
> 43: A
> 40: B>C
> 6: C>B
> 1: C
> 10: D
>
> ... I think that a case can be made for either A or B. After all,
> they'd be tied if we try to approximate Score by using truncatable
> Borda here. But no serious case can be made for C or D, even
> though C wins MTA and MCA.
>
> Anyway, I think U/P does a better job trying to discourage the
> kind of strategy that would lead to a scenario like the above. And
> part of that is the default rule which Chris has criticized.
>
> One possible alternative default rule: ballots alternate between
> defaulting to "acceptable" and to "unacceptable". Each ballot
> clearly states which default it uses, and there is a place on the
> ballot to globally change that default. (I doubt Chris will like
> this idea, but it is at least straightforward, explicit, and easy
> to describe.)
>
>
> Chris Benham
>
>
>
>
>
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