Hi Jameson,
--- En date de : Mer 23.6.10, Jameson Quinn <[email protected]> a écrit :
>3a. Quasi-elimination. I believe that winning-votes Condorcet methods,
>like Schulze, are an attempt to ensure that A wins even in the face of
>B's truncation. However, this only works if C voters truncate rather than
>splitting evenly between CBA and CAB. Other stronger quasi-elimination
>systems that I know of have IRV-like problems.
I would say that WV methods attempt to ensure that {A,B} wins even in
the face of B's truncation. Making A win despite truncation will often be
impossible without violating Plurality (e.g. with MMPO).
>4. Runoff. Viewed in an outcome-oriented game-theoretic vacuum, this is
>just the same as elimination, and it suffers the same problems. However,
>if voters have some negative utility for the runoff itself, then a system
>can use the threat of one to motivate honest voting in the first round.
>Since the scenario assumes that there is a clear winner with no cycles
>under honest voting, that may be enough.
I see the use of leaving no purpose for insincerity in the second round.
For example supporters of candidate C may find it too risky to give a
second preference to one of the opposing clones, but once C has been
removed from consideration, there's no more disincentive.
It's not quite clear to me how to use a runoff to ensure sincerity in
the first round, in general.
I think I would just look at the outcomes for all important scenarios and
categorize that way: Say the candidates are C, A, B in descending order
of bloc size. C voters always truncate. A and B blocs give a second
preference to each other, or to no one.
Then you have:
A and B both truncate: Everything will elect C.
Neither A/B truncate: Almost everything will elect A. (Ignore FPP)
A truncates only: Some methods elect C, some A.
B truncates only: A B or C will win.
Without supposing anybody gets a second chance to express preferences,
there are only six possible methods, based on the last two scenarios.
CA: ?
CB: ?
CC: DSC, SPST, VFA
AA: WV, Bucklin, Approval, and many many other methods
AB: Raynaud(wv), MMPO with ties broken by FPP
AC: IRV, QR
So I guess that broadly there should only be up to four treatments or so.
Other than runoffs, another way to manipulate the ballot format in order
to encourage a different outcome is to use "votes against," so that
rather than cooperating with the fellow clone, they just incidentally
both oppose the same frontrunner.
Kevin Venzke
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