[EM] IRV & Spoiler Effect

[Markus Schulze]

Hallo,

Eric Gorr wrote (12 May 2004):

> Well, what would you say is the difference between a
> spoiler and a clone? At the moment, I cannot see any
> difference.
>
> It would seem that for candidate A to be a spoiler for
> candidate B, it would seem that A & B would need to be
> clones. Therefore, for a ranked ballot method where
> people are voting sincerely, A & B would be ranked
> close to each other. So, so long as the method is
> clone-proof it would also be spoiler free.

Some people when they use the term "spoilers" talk about Tideman's
concept of "clones". Some people when they use the term "spoilers"
talk about Arrow's concept of "irrelevant alternatives". Therefore,
when someone uses the term "spoilers" without giving additional
information it is quite unclear what he is talking about.

******

Dave Ketchum wrote (24 July 2003):
> While IRV gets away from most of Plurality's spoiler problems,
> it has a few of its own. Condorcet simply DOES NOT DO spoilers.

I wrote (24 Jul 2003):
> The problem is that IRV supporters when they use the term
> "spoilers" usually mean "clones" (due to Tideman's terminology)
> while Condorcet supporters when they use the term "spoilers"
> usually mean "irrelevant candidates" (due to Arrow's terminology).
> I have observed IRV supporters and Condorcet supporters discussing
> for hours without even noticing that they were discussing different
> kinds of "spoilers."

Markus Schulze