[EM] Ranked Pairs

Forest Simmons forest.simmons21 at gmail.com
Sun Sep 17 21:17:37 PDT 2023

On Sat, Sep 16, 2023, 9:42 PM Michael Ossipoff <email9648742 at gmail.com>

> 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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