[EM] Beatpath vs Ranked-Pairs

Michael Ossipoff email9648742 at gmail.com
Thu Oct 24 17:43:27 PDT 2013

Hi Jobst--

I've just read your EM postings for April and May of 2004.

I couldn't find the simulation report. What did the simulations say
about River vs Ranked-Pairs?

Does this accurately describe the difference between River and Ranked-Pairs?:

When River is described in language like that in RP's definition, as I
understand it, River additionally rejects a defeat if the defeated
candidate already has an already-kept defeat that is stronger?

...the justifictation being that if s/he is already defeated, then
there's no need for hir new defeat.

And, not having that unnnessary defeat can avoid the unnecessary
rejection of some subsequent new defeat(s).

If that's right, then I understand the justificaton of River, in
comparison to Ranked-Pairs.

What are the differences in strategy-properties or strategy-guarantees
or strategy vulnerabilitie, between River and  Ranked-Pairs.

Would it be right to say that River is Ranked-Pairs, with an
additional reason for rejecting a newly-considered defeat?

That would mean that River is almost as simple as RP. What are its
strategic advantages over RP?

Michael Ossipoff

(I call myself "Michael" now, instead of "Mike", because at least 2
people have told me that it sounds better.)

On Thu, Oct 24, 2013 at 5:15 PM, Jobst Heitzig <heitzig-j at web.de> wrote:
> Dear all,
> I'd be really happy if you cared to consider also the River method when
> comparing Ranked Pairs and Beatpath. As you cite Steve's simulations,
> you might want to look at my April 24, 2004, post
> (http://lists.electorama.com/pipermail/election-methods-electorama.com/2004-April/012772.html),
> where I discussed their relationship and performed similar simulations
> showing that indeed River is a very good compromise between Ranked Pairs
> and Beatpath in terms of criteria.
> Best,
> Jobst
> Am 24.10.2013 20:23, schrieb Michael Ossipoff:
>> When  say "Ranked-Pairs" or "RP", I'm referring to the practice of
>> considering the pairwise defeats in order of their strength, keeping a
>> considered defeat if it isn't contradicted by already-kept defeats
>> (directly,or by being in a cycle with them).
>> Additionally, I'm referring to versions of RP that allow equal
>> ranking, and allow trunction, and judge defeat-strength by
>> winning-votes.
>> I'm not concerned about how ties ae dealt with, because, publc
>> political elections are the important voting-system appication, and
>> ties will vanishingly-rare in such elections.
>> I've already said some of this, but I'm now adding a little.
>> In that comparison, Beatpath is easier to program, and somewhat faster
>> to compute (but computation-time is negligible wth today's computers,
>> for either method).
>> Those attributes make Beatpath appealing for organizations.
>> But Ranked-Pairs is incomparbly more briefly-defined, and makes a lot
>> more sense, and is more easily and obviously motivated and justsified,
>> when proposing it to people.
>> Additionally, Steve Eppley's simulations found that, when RP and
>> Beatpath choose different winnes, the public colletively prefer RP's
>> winner to Beatpath's winner, overwhelmingly more often than
>> vice-versa.
>> In other words, anyone advocating Beatpath over RP needs to explain
>> why we should want a less demcratic voting-system.
>> I emphasize that, due to their chicken-dilemma, I don't advocate
>> either RP or Beatpath for public political elections in the U.S.
>> Instead, for the Green scennrio, I advocate Benham and Woodall, though
>> IRV would be acceptable, even though it has disadvantages (previously
>> described by me), in comparison to Benham and Woodall.
>> Michael Ossipoff
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