[EM] SSD is not BeatpathWinner
nkklrp at hotmail.com
Mon Dec 22 23:54:02 PST 2003
Markus often says that BeatpathWinner is the same as Cloneproof SSD (CSSD)
and SSD. Actually no. SSD is a different method that can have different
outcomes when there are pairwise ties.
It's true thatr CSSD and BeatpathWinner are equivalent, always give the same
In public elections, where pairwise ties are vanishingly rare, SSD chooses
the same as CSSD, which means that, under those conditions, SSD chooses the
same as BeatpathWinner.
But, aside from how they choose, there's an important difference between SSD
and BeatpathWinner: Proposability.
SSD's definition, with its innermost unbeaten sets, is naturally and
obviously motivated and justified. Innermost unbeaten sets are compelling.
BeatpathWinner's count rule has an arbitrary quality. It wouldn't have the
acceptability of SSD. Or the acceptability of Ranked-Pairs either.
Maybe when Markus names those methods as being the same as BeatpathWinner,
he'd like to take credit for all of them (assuming for the moment that he
really did invent BeatpathWinner). Yes he did describe CSSD after proposing
BeatpathWinner, pointing out the equivalence. But I doubt that he proposed
SSD was a colaboration from discussion with Steve Eppley. Neither of us knew
of Markus's CSSD description at that time. Later, in a discussion in which a
clone-independent method was desired, and in which someone else was
proposing BeatpathWinner, a method not as obviously justified as SSD, I
changed SSD to make it clone-independent--Cloneproof SSD (CSSD). Later I
found out that Markus had described CSSD.
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