On Mar 10, 2010, at 7:08 AM, robert bristow-johnson wrote:
thanks, Chris. i will ponder this. i understand RP and (i think)
Schulze, at least how the mechanisms go, but i'll admit i haven't
been as invested in *how* to resolve cycles or *which* Condorcet
method is best as much as i am invested in (some) Condorcet vs. IRV
vs. FPP or two-round runoff. the reason is that i am skeptical of
the likelihood of a real election with thousands of voters going
into a cycle.
considering both the objective advantages of Schulze and the
simplicity of Ranked Pairs, i think that if Condorcet would ever be
sold to the general population as a method to decide elections for
government, i would suggest Ranked Pairs. but maybe it should be
IRV (if a cycle) or something wild-assed. whatever will be needed
politically to get people to buy into Condorcet.
maybe it is, but i don't think that is the same mistake as, when the
Ranked Ballot is introduced to folks in Vermont or Minnesota or San
Francisco or North Carolina, attaching that ranked ballot to the IRV
method of tabulation. that was a mistake and it doesn't serve as a
stepping stone to better elections with Condorcet (because of
entrenchment of IRV supporters and, i believe, a near certainty of
IRV displaying anomalies that turn everyone off of IRV and, by
association, the Ranked Ballot).
so, keeping RP, Schulze in mind for later, what would be a "good"
scheme for resolving cycles by use of elimination of candidates?
what would be a "good" (that is resistant to more anomalies) and
simple method to identify the "weakest candidate" (in the Smith set)
to eliminate and run the beats-all tabulation again? i'm not saying
elimination is a good way to do it, but it might be easier to sell
to neanderthal voters.
All methods have some weaknesses that can be used against them in the
marketing battle. So maybe the challenge is to build a solid campaign
that is convincing enough to neutralize all emerging fears and failure
examples.
Schulze method is quite convincing since it is already in use in many
places. (I'm not sure it is objectively better than ranked pairs and
others although it is certainly a good method.) Ranked pairs can be
easily described as a method that sequentially confirms pairwise wins,
so it is almost as natural and straight forward sequential algorithm
based as IRV (although it is a bit more complex in the sense that it
compares pairs instead of single candidates when making the sequential
decisions). And there are also simpler Condorcet methods like
minmax(margins) that simply counts the number of additional votes each
candidate would need to beat all others.
I'm not aware of any sequential candidate elimination based method
that I'd be happy to recommend. One can however describe e.g.
minmax(margins) in that way. Eliminate the candidate that is worst in
the sense that it would need most additional votes to win others, then
the next etc. In the elimination process one would consider also
losses to candidates that have already been eliminated (I wonder if
this approach makes it less "natural looking" than the elimination
process of IRV).
But as said, maybe the key is to arrange a solid campaign. You can
surely e.g. find lots of election method experts that are happy to
agree that Condorcet methods are the best for some city for some need
and best single winner methods (for competitive elections) in general.
But quite certainly there will be also experts that think otherwise.
And there is certainly a risk that all the Condorcet friendly experts
will use different argumentation, may disagree on details and as a
result will confuse the audience. Maybe one should start from
Scientific American etc. to first firmly establish the idea that
Condorcet methods indeed are the de facto state of art methods (and
practical too). IRV campaigns have been successful, so I wonder why
Condorcet campaigns could not follow (maybe Burlington needs a timeout
now but not much more, and other cities could take steps forward
already now and support Burlington that way).
(I have to add that if people want to keep the USA as it mostly is, a
two party based system, then I must recommend FPTP :-). And if not,
then maybe also some additional (maybe proportionality related)
reforms are needed.)
Juho
r b-j
On Mar 9, 2010, at 11:45 PM, C.Benham wrote:
Robert Bristow-Johnson wrote (5 March 2010):
i like Ranked Pairs best, too. and if the Smith Set are three
candidates, it and Schulze pick the same winner.
> Bringing Plurality in would be a distraction, since we have no
need
> to go near this method and risk a worse answer.
it's a "worse answer" in a weird circumstance where an argument
could be made that any in the Smith set have
some reasonable claim or legitimacy to be elected. why not the guy
with the most votes?
Interpreting "most votes" as 'top-ranked on the greatest number of
ballots', the answer is that the resulting method
fails the Clone-Winner and Minimal Defense criteria.
49: A
24: B
27: C>B
A>C 49-27, C>B 27-24, B>A 51-49
More than half the voters have ranked B above A and A no higher
than equal bottom, and yet Smith,FPP elects A.
The Ranked Pairs and River and Smith//MinMax and Schulze
algorithms, using Margins as the measure of defeat
strength (referred to collectively as "Margins") and IRV also
elect A.
Say we replace A with a set of clones, A1 and A2.
26: A1>A2
23: A2>A1
24: B
27: C>B
(A2 > C > B > A1 > A2)
Now Smith,FPP elects C violating Clone-Winner. Those other methods
I mentioned meet Clone-Winner and so
elect one of the clones (A1).
The number of people (ballots) that voted for (ranked above equal-
bottom) the clones and not C exceeds the number
that voted for C, and yet C wins violating my suggested "Strong
Minimal Defense" criterion.
Chris Benham
http://wiki.electorama.com/wiki/Minimal_Defense_criterion
http://nodesiege.tripod.com/elections/#critmd
http://nodesiege.tripod.com/elections/#critclone
Douglas Woodall splits Clone Independence into "Clone-Winner" and
"Clone-Loser".
Clone-Winner says that if winning candidate X is replaced by a set
of clones than the winner must come from that
set. Clone-Loser says that the winner shouldn't change if one (or
more) losers are replaced by a set (or sets) of clones.
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