[EM] Cloneproof SSD

[MIKE OSSIPOFF]

> > But A has beatpaths to C & B, and neither has a beatpath to A.
> >
> > Doesn't a beatpath have to consist only of pairwise defeats?
> > Taken literally, a beatpath is a path of beats, not ties.
>
>To guarantee that LIIAC is met, it is only necessary that a beat
>path consists of wins or ties. It is not necessary that a beat path
>consists only of wins.

Sure, but a tie still isn't a "beat", and doesn't seem properly
part of a beatpath.

>You wrote (23 Jan 2001):
> > Then there's the fact that, in small committee votes, Tideman will
> > sometimes embarrass us by choosing outside the Schwartz set. Not
> > a serious problem, but definitely an aesthetic gaffe.
>
>I don't consider a violation of the Schwartz criterion to be
>"definitely an aesthetic gaffe." To my opinion, it is more
>important that as few voters as possible are overruled. In the
>example above, candidate A is rejected by 50 voters in his worst
>pairwise comparison while candidate C is rejected only by 40
>voters in his worst pairwise comparison.
>
>The Schwartz set heuristic unnecessarily chooses winners whose worst
>pairwise comparison are strong. This is caused by the fact that
>the Schwartz set heuristic doesn't take the "strengths" of pairwise
>ties into consideration.

A tie has no strength as a defeat. Voters in a tie aren't overruled
no matter what happens. The voter who is overruled is the voter who
voted for a defeat of the winning candidate.

>
>******
>
>Blake wrote (17 Jan 2001):
> > Here's my problem with that.  I agree that we have to drop defeats.
> > I also agree that we should not drop defeats unnecessarily.  However,
> > the process of iterating Schwartz imposes some requirements.  We
> > often have to drop defeats just to keep the process going.  So, we
> > might have to drop defeats that would be unnecessary to drop if we
> > only wanted to impose consistency.
> >
> > It's a similar problem to IRV.  Obviously some candidates are going
> > to be dropped (in the sense that not all candidates can win).
> > It's also obvious that if you only look at first place votes among
> > non-dropped candidates, that IRV picks the right candidate to drop.
> > However, if we don't assume these restrictions, it isn't clear that
> > IRV is dropping the right candidates.
>
>I consider iterative heuristics to be less intuitive than non-iterative
>heuristics. The problem with iterative heuristics is: Even when we know
>that this heuristic works properly in each step, we still don't know
>whether the final winner is the right candidate.

True, Condorcet's obvious motivation is only at the step level.
"We have mutually contradictory defeats; what shall we do?" "Drop the
weakest defeat, and check whether we have an undefeated candidate
(or, in Cloneproof SSD, a cycle-free Schwartz set)."

SSD, Cloneproof SSD, and BeatpathWinner all can be justified in terms
of criteria. SSD's obvious motivation is only at the step level.
But BeatpathWinner has none. So, though SSD doesn't have the
kind of motivation that we might like it to have, for the overall
process, rather than one step at a time, at least it has some kind
of natural motivation. As I said, I explained SSD to someone who'd
had no prior experience with voting systems, and she had no trouble with
it. It was obvious to her. That wasn't true with SD, due to its
mention of cycles. With SD, she didn't hesitate to say that something
about the definition (the cycles) didn't make sense to her. When I
told her about DCD, which says to simultaneously drop each cycle's
weakest defeat, she immediately said "But you just want to elect one
candidate...". She saw right to DCD's problem, its tie-proneness.

I'll ask about BeatpathWinner next.

Sure, I haven't done wider polling, but neither have any of us.

As for cycles being counterintuitive for people, I emphasize that
, for a public proposal, I'd propose ordinary SSD, rather than
Cloneproof SSD. Ordinary SSD doesn't mention cycles.

>
>I also think that -in so far as there is no general idea behind
>the Schwartz set heuristic- too many details have to be explained.
>Example: It isn't clear why only circular ties between current Schwartz
>winners were contradictory; to my opinion, circular ties are always
>contradictory.

It's not that they aren't contradictory. It's that the defeats
of non-Schwartz-set candidates by Schwartz set candidates aren't
contradicted. Those defeats stand. Those candidates lose. What
do we care if there are contradictory defeats among candidates who
lose anyway, due to uncontradicted defeats?


>
>******
>
>You wrote (21 Jan 2001):
> > I no longer advocate Tideman, but as I define it, Tideman terminates
> > as soon as there are no more cycles. Doesn't the standard wording
> > terminate as soon as every defeat has been either skipped or locked?
> > But I emphasize that I no longer advocate Tideman, because Cloneproof
> > SSD seems so much better for small committees, and because even ordinary
> > SSD does better in public elections (where its clone-criterion
> > violation has negligible likelihood).
>
>What does Steve Eppley say about the fact that you don't promote the
>Tideman method any more?

I haven't heard from Steve lately. No doubt he'd disagree with me on
that. But I want to re-emphasize that the merit differences between
different BC complying methods aren't really important. So I don't
consider SSD vs BeatpathWinner vs Tideman to be a major issue, merit-wise. 
Of those, SSD is what I consider the best public proposal, but
they're all very good.

But I don't know what the properties of your version of BeatpathWinner
are, the one that counts pair-ties as defeats.


Mike Ossipoff


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