On Jan 21, 2010, at 2:29 AM, Kristofer Munsterhjelm wrote:
robert bristow-johnson wrote:
i think that the answer is "no", if a Condorcet winner exists and
that all bets are off if a CW does not exist, except, perhaps for
these "strategy-resistant" methods such as Markus Schulze's
method. i sorta understand it, but since he hangs here, i think
Markus should address the question if the Schulze method is
spoiler free.
MAM/Ranked Pairs is also pretty strategy-resistant and is easier to
understand. Schulze has the advantage of producing better results
in some cases (closer to Minmax), but if "ability to describe to
the public" is important, then Ranked Pairs wins there.
Could someone please provide me with an example of the spoiler
effect occuring with the Condorcet method of counting rank
choice ballots or tell me why the spoiler effect doesn't happen
with Condorcet in a few words?
(...)
i would say that (with the CW existing), it's spoiler-proof.
Yes. If there's a CW and a candidate is added, and that candidate
doesn't create a cycle, then the winner doesn't change.
and if that candidate that is added doesn't *win*. a spoiler is
*not* a winner that when removed from the election and all ballots
does not change who the winner is. a spoiler must be a loser to the
election, whose presence changes who the winner is. i remember
reading someone's poor attack on IRV (in local Burlington blogs) that
claimed that Bob Kiss (who won Burlington's IRV election) was a
"spoiler". they were misusing or misunderstanding the concept of a
3rd-party candidate. (maybe somewhere else, a 3rd-party candidate
can only hope to be a spoiler, but in Burlington a 3rd-party
candidate can expect to win office once in a while. that's a little
different.)
so, we have a CW... add a candidate, if that candidate does not
become the winner, nor cause a cycle, then the Condorcet Winner we
had before continues to be the CW with the added candidate. (boy, i
guess we're rephrasing the same thing multiple times!)
All the "tricky" stuff happens when there is a cycle, or the
candidate makes one.
yup.
The advanced methods can claim further resistance: Schulze and
Ranked Pairs both make their winner decision independent of
candidates not in the Smith set.
this, i understand...
River is independent of Pareto-dominated alternatives - a candidate
is Pareto-dominated if everybody who ranks both him and some other
(specific) candidate, rank the other candidate above him (e.g. X is
Pareto-dominated by Y if all voters who rank both X and Y say Y>X,
and there's at least one such voter).
i wouldn't mind if someone explains this. i don't know what "Pareto-
dominated" is about. can someone expound?
I imagine these resistances would mostly come into play in smaller
elections. Still, they're nice to have, and their existence
immediately tells parties not to try exploiting certain weaknesses
(because it won't work).
yes, that's the whole point. this is why i am not yet afraid of
someone strategically voting to push a Condorcet election into a
cycle. it would be an unsafe way to accomplish a political goal.
how could anyone predict what would happen?
--
r b-j [email protected]
"Imagination is more important than knowledge."
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