[EM] Truncation dilemma

[Jameson Quinn]

2010/6/23 Kevin Venzke <stepjak at yahoo.fr>

> Hi Jameson,
>
> --- En date de : Mer 23.6.10, Jameson Quinn <jameson.quinn at gmail.com> 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 am not saying that a runoff "threat" can ensure sincerity in the first
round in general. I am only speaking of this one scenario. If I were to
generalize, I think that runoffs can help prevent insincere Condorcet
cycles, but can do nothing about real ones. I think that's enough, because I
suspect that insincere ones are more common.

Incidentally, any runoff methods which works for this purpose would
eliminate one of the clones (probably B) and leave A facing C, not B, in the
runoff. Methods which eliminate C depend on cooperation from A and B - and
thus eliminate A when B doesn't cooperate, which defeats the purpose.

JQ
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