[EM] Condorcet cyclic drop rule

[MIKE OSSIPOFF]

>From: "MIKE OSSIPOFF" <nkklrp at hotmail.com>
> > When Mr. Condorcet made his proposals, he specified that defeats be
> > measured by defeat-support. And that's the only defeat measure that
> > confers compliance with the defensive strategy criteria.
>--snip--
> > Ranked-Pairs(defeat-support) is something that Condorcet proposed,
> > and it meets all 4 of the majority defensive strategy criteria,
> > as does Cloneproof SSD.
>
>Of course Condorcet didn't really propose Ranked-Pairs
>(defeat-support).  That method was invented recently by Mike, based on
>the method Tideman invented around 1985.  Condorcet wrote in the
>1700's.

Wrong. Condorcet wrote around the 1780s or 1790s.

Invented recently by Mike? Steve Eppley defined it before I did.
But thanks for trying to give me credit for that better version.

Whether Condorcet "of course" didn't really propose
Ranked-Pairs(defeat-support) depends on whether you're correct in what
you're saying below in this message that I'm replying to.

>
>Subject: Re: [EM] Condorcet cyclic drop rule
>Date: Wed, 28 Mar 2001 03:26:23 -0000
>
> > Defeat Support is what Condorcet himself specified. Norm & Markus
> > posted quotations about that. They're in the archives for last year.
>

>It isn't a complete translation of his works.  Unfortunately, one
>important section is merely described, instead of being presented as a
>translation.  However, I think it proves my case.

No, I don't think that something that is a transcription, and not a
translation, proves anything.

>
>Here are some back-ground quotes.  These are by Condorcet (although
>they are translated).  He uses the term plurality as we might use the
>term majority today.
>
>For example, p 137 "An Essay on the Application of Probability Theory
>to Plurality Decision-Making" 1785
>
> > The Proposition `A is better than B' therefore obtains 41
> > votes to 40.
>
>p 126
> > the first of which has a plurality of 37 votes to 23, and
> > the second a minority of 29 against 31
>
>p 136
> > it would seem more reasonable to judge these propositions,
> > not according to the preceding hypothesis, but according
> > to the degree of plurality they have obtained.
>
>The preceding hypothesis is that of Borda.  I present these to show
>that Condorcet talks about the "degree of plurality" as being the
>deciding point.  He seems to speak of pluralities as a pair of values,
>however.  Norm's argument was that at the time plurality strength
>would have been measured by the number on the winning side, and he
>gave a quote from a French dictionary of the time in support of this.
>Norm reasoned that Condorcet must have meant winning-side voters by
>"degree of plurality".

So instead of going by the French dictionary of Condorcet's time, you'd
rather use your own interpretation.


>
>I argued that since no one had come up with an example where Condorcet
>had considered incomplete rankings, he hadn't.

Unless Condorcet can be brought here in Tom's time machine, only
a claravoyant can tell us what he was thinking. It seems most reliable
to go by what he said, and what it means according to a  French
dictionary of his own time.

  So, even if he did say
>to only use winning-side voters, this wouldn't have mattered because
>he wasn't comparing margins to winning-votes.

Is that your claravoyant ruling?

>And that he expected these ballots to be complete:
>
>p 123 "Essay..."
> > In general, therefore, we should replace this method with
> > one in which each voter simultaneously shows his preferences
> > among all the candidates by placing them in order of merit.

Maybe he expected that, but it seems reasonable to define "Condorcet's
method" as something consistent with his defeat wording, rather than as
something different.

>The point is that Condorcet's formula, called Condorcet's jury
>theorem, relies on margins, h-k.  So, Condorcet not only specifies
>margins

I must have missed the part where you quoted the translation of
Condorcet specifying margins as the measure of the strength of a
pairwise defeat.

, but his whole probabilistic argument makes no sense, unless
>you realize he is talking about margins.

That formula that you quoted, that isn't from Condorcet's definition
of his voting system proposal, is it. If that formula is how you
determine candidates' probability of being the best, and he doesn't
use that formula in his method definition, then why should that formula
imply that margins are intended in Condorcet's method definition? Sure,
margins are used in that formula, but that formula isn't part of
Condorcet's method, the voting system proposal.

Maybe we're presuming a bit when we want to overrule the dictionary
that describes usages in Condorcet's time.

Mike Ossipoff

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