[EM] Fwd: Ranked Pairs

Colin Champion colin.champion at routemaster.app
Mon Sep 18 07:02:38 PDT 2023

Thanks to Kevin and Michael for pointing out a feature of minimax I was 
unaware of. I had however seen Richard Darlington's paper [1] in which 
he referred to 'several studies' comparing margins with winning votes. 
He reports that margins 'was the big winner in all of them'. I suppose 
I'll have to look deeper.
[1]. https://arxiv.org/abs/1807.01366

On 18/09/2023 07:57, Michael Ossipoff wrote:
> ---------- Forwarded message ---------
> From: *Michael Ossipoff* <email9648742 at gmail.com 
> <mailto:email9648742 at gmail.com>>
> Date: Sun, Sep 17, 2023 at 22:54
> Subject: Re: [EM] Ranked Pairs
> To: Forest Simmons <forest.simmons21 at gmail.com 
> <mailto:forest.simmons21 at gmail.com>>
> This was meant to be sent by “Reply All”, in order to post it. So now 
> I’m forwarding it to EM.
> Forest—
> But wv prevents truncation (strategic or otherwise) from taking the 
> win from a CW.
> …&, with, wv, refusing to rank anymore you don’t approve will cause 
> offensive order-reversal by their preferrers to backfire.
> I’d always take that precaution, & would advise others to.
> When we discussed these guarantees years ago they seemed absolute, & 
> we still have the guarantee-criteria based on them…met by wv versions 
> of MinMax, RP, CSSD, & Smith//MinMax.
> …&, with MinMax, whose winner can come from anywhere, not just from 
> the top-cycle, & so, offensive order-reversal, when there are a fair 
> number of candidates, is unpredictable & risky for its perpetrators, 
> even if the precaution of deterrent-truncation isn’t taken.
> On Sun, Sep 17, 2023 at 21:17 Forest Simmons 
> <forest.simmons21 at gmail.com <mailto:forest.simmons21 at gmail.com>> wrote:
>     On Sat, Sep 16, 2023, 9:42 PM Michael Ossipoff
>     <email9648742 at gmail.com <mailto:email9648742 at gmail.com>> wrote:
>         Is that RP(wv), or RP(margins) ?
>         RP(wv) would thwart & deter offensive strategy, an important
>         property in public elections.
>         …&, actually, it seems to me that MinMax(wv) would do that better.
>         That’s because, choosing only from the Smith Set RP, limits
>         it’s choice to the strategic top-cycle that created by the
>         offensive strategists.
>         Suppose that the CW’s preferrers don’t do defensive truncation
>         (never rank anyone you wouldn’t approve in Approval, or whose
>         preferrers you regard as likely to offensively order-reverse) ?
>         Knowing that RP will limit its choice to their small
>          strategic top-cycle, it would be easier for the strategists
>         to be fairly sur that their candidate would win in that top-cycle.
>         But, with MinMax, the winner is chosen more broadly, & could
>         be anywhere in the candidate-set.  …making it more difficult &
>         risky to confidently do offensive order/reversal.
>         RP(margins) might the best choice for a completely honest
>         electorate, but MinMax(wv) seems better for public elections,
>         due to its better thwarting & deterrence of offensive strategy.
>         Yes, MinMax doesn’t meet the luxury cosmetic look-good
>         criteria that RP meets.
>         But for one thing, I remind you that natural ( sincere)
>         top-cycles are vanishingly-rare.
>     This is the same conclusión I have come around to.
>     And methods that break a three member top cycle at the weakest
>     link tend to reward the burier faction.
>         So do you want to have less strategy-protection, in order for
>         the result to maybe look better in a vanishingly rare natural
>         top/cycle?
>         …& how bad is a violation of Condorcet-Loser anyway.  “Beaten
>         by all the other alternatives” sounds like some kind of
>         unanimity, but of course it isn’t. It isn’t like a
>         Pareto-violation. I remind you that the MinMax winner has
>         fewer voters preferring some particular candidate over him
>         than anyone else does.
>         Clone-Criterion violation? How bad that really in MinMax,
>         especially when we’re talking about a vanishingly rare natural
>         top-cycle?
>         RP(margins) for a completely honest electorate.
>         MinMax(wv) for public elections.
>         ..& about a primary to reduce the candidates to 5: Forget the
>         primary. If you think people will have trouble rank-ordering
>         lots of candidates, I remind you that, to vote among them in a
>         primary, they’d still have to examine & choose among the
>         initial many candidates.
>         …harder than ranking only the ones you know & regard as
>         deserving & definitely in your accepts& preferred set.
>         On Wed, Sep 13, 2023 at 00:18 Colin Champion
>         <colin.champion at routemaster.app
>         <mailto:colin.champion at routemaster.app>> wrote:
>             I notice that RP is the only election method mentioned by
>             name in the
>             Virginia agenda.
>             A while ago I ran some simulations on elections with
>             truncated ballots.
>             Something I noticed was that the presence of RP in the
>             list of methods
>             made the software unacceptably slow. I didn't look into
>             the cause, but
>             there's a natural explanation, which is the fact that RP
>             is known to be
>             NP-complete when it deals correctly with tied margins,
>             i.e. by
>             exhausting over all their permutations. Presumably if some
>             candidates
>             are unpopular and ballots are extensively truncated, then
>             tied margins
>             are much likelier than with complete ballots.
>             I gather that practical implementations of RP choose a random
>             permutation rather than exhausting. This seems to me to
>             bring a danger.
>             The presence of a few vanity candidates (truncated off
>             almost all
>             ballots) may lead to ties, and this may lead to a
>             comfortable winner
>             looking as though he owes his victory to a coin-toss.
>             Obviously this
>             undermines the legitimacy of his win.
>             CJC
>             ----
>             Election-Methods mailing list - see
>             https://electorama.com/em <https://electorama.com/em> for
>             list info
>         ----
>         Election-Methods mailing list - see https://electorama.com/em
>         <https://electorama.com/em> for list info
> ----
> Election-Methods mailing list - see https://electorama.com/em for list info

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20230918/3dfc0411/attachment.htm>

More information about the Election-Methods mailing list