[EM] Reply to James Green-Armytage--Condorcet strategy
nkklrp at hotmail.com
Fri Dec 26 23:23:01 PST 2003
That's a big subject.
You correctly point out that defensive strategy is a worse problem with
margins than with winning-votes (wv).
Additionally, with wv, truncation can't steal the election from a
well-supported CW, a CW who has a majority defeat against the truncators'
candidate. That's the subject of the criterion SFC. GSFC generalizes SFC to
situations where there's no CW. When defeats are measured by wv, then SSD
and Ranked-Pairs meet the powerful GSFC. Plain Condorcet (PC) meets SFC.
In fact, SFC and GSFC describe plausible conditions under which, with
complying methods (Condorcet wv), the majority who don't want X can be sure
X won't win, _without having to do anything other than vote sincerel_.
That's what I most like about Condorcet wv.
Your iniltial wording of the Condorcet count implies that defeats are
measured by margins. That probably isn't intentional.
To put the problem in perspective, Condorcet wv has no defensive strategy
need unless someone is going to try offensive order-reversal strategy. At
its very worst, under less-than-likely worst-case conditions, Condorcet wv
begins to share the strategy need that the other methods have all the time.
And, with Condorcet wv, in order for you to successfully steal the election,
it's only possible if the people from whom you're stealing the election have
tried to help you. Doesn't that make you feel proud of yourself? :-)
P.S. Don't expect them to rank your cxandidate again. Don't expect your
winner to be able to show his face in public.
As you mentioned, it's like a game of chicken, when defensive truncation is
threatened against would-be offensive order-reversers.
But please note that the supporters of the middle CW who is being protected
will suffer less if no one chickens out, compared to how much the offensive
order-reversers would suffer then. That's because, in your example, the C is
farther away from the order-reversers than from the defenders.
Additionally, a defender has a more credible threat. A cat defending its
territory has a more credible threat against an interloper than the other
cat has. The defender, it's understood, is more willing to fight and risk
getting hurt when defending what's rightfully his. This adds to the
defenders' advantage in the game of chicken.
Sure, if no one chickens out, the result isn't desirable for the defenders
either. Defensive truncation is a dominated strategy for them: But note that
dominated deterrent strategies are common in legal systrems and in the
animal kingdom. They wouldn't be used so much if they didn't work.
In public elections, effective offensive order-reversal would require public
organizing. There' s just no way it could be done without its intended
victims hearing about it and using defensive truncation.
So in public elections, offensive order-reversal is a losing proposition.
For all the above reasons, I don't consider offensive order-reversal a
problem. Effectively, then, Condorcet wv is practically strategy-free.
Remarkably strategy-free. No other method of comparable simplicity even
So, for that reason, I don't feel that it's necessary to include
enhancements to further reduce that already near-nonexistent problem.
Of course, when Condorcet wv has been in use for a long time, and if by then
people are discussing the order-reversal possibility, then, at that time,
the anti-reversal enhancements could be proposed.
Even though I claim that they aren't needed in public Condorcet wv
proposals, I'm going to discuss anti-reversal enhancements in a subsequent
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