[EM] Fwd: Ranked Pairs

Wed Sep 20 18:35:40 PDT 2023

I think that if you were looking at the success rates of unilateral burial
options along with the basic burial defense of truncation below sincere CW
... then the difference between Winning Votes and Margins would be more
striking (still in favor of wv).

On Wed, Sep 20, 2023, 2:12 PM Michael Ossipoff <email9648742 at gmail.com>
wrote:

> Thanks for the experiment. I hope that Tideman’s organization won’t be
> promoting the old margins version of RP.  …unless just for maybe choosing
> between pizza-toppings or movies.
>
> On Wed, Sep 20, 2023 at 07:30 Colin Champion <
> colin.champion at routemaster.app> wrote:
>
>> Well, I coded up Minimax(WV) for my own evaluation. Rather to my disgust
>> (and contrary to Darlington) I find that it does indeed outperform Margins
>> for truncated sincere ballots. I ran a large number of trials with 10001
>> voters under a spatial model, 8 candidates being truncated to 4. Minimax
>> (margins)=83.35% correct, minimax(wv)=84.09%. Other methods which
>> outperformed standard minimax in the simulation include Approval Sorted
>> Margins (in an ordinal version suggested by Ted Stern): 84.14%; Black:
>> 84.22%; Smith,Borda: 84.22%.
>>    Hastily written and unreliable code, not to be trusted.
>>       CJC
>>
>> On 18/09/2023 22:30, Michael Ossipoff wrote:
>>
>> Hi Colin—
>>
>> Yes, margins beats wv for social-utility under sincere voting when
>> there’s that vanishingly rare natural top-cycle.
>>
>> But Darlington & Tideman evidently aren’t considering resistance to
>> offensive strategy, which is a much bigger threat than natural top-cycles.
>>
>> Protecting the CW from offensive strategy is more important than SU in
>> natural top-cycles.
>>
>> …& is better for SU.
>>
>> On Mon, Sep 18, 2023 at 07:03 Colin Champion <
>> colin.champion at routemaster.app> wrote:
>>
>>> 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.
>>>    Colin
>>> [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>
>>> Date: Sun, Sep 17, 2023 at 22:54
>>> Subject: Re: [EM] Ranked Pairs
>>> To: Forest Simmons <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>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Sat, Sep 16, 2023, 9:42 PM Michael Ossipoff <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> 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
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>>>>>>
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