[EM] IRV & Spoiler Effect

[wclark at xoom.org]

Eric Gorr wrote:

> If this is true, no ranked ballot method can be free from the spoiler
> effect, but do we not generally claim that the better Condorcet
> methods are spoiler free?

Condorcet is sometimes claimed to be spoiler free because it can satisfy
what RobLa called "relaxed versions of IIAC, such as Local IIAC."

Full IIAC (which does indeed capture the spirit of the spoiler effect) is
argued to give Condorcet trouble only when there is an actual ambiguity in
the will of the electorate, e.g. cycles.  In all other circumstances
(characterized by "Local IIAC" or its variants) Condorcet actually passes.

Whether or not you concider cycles in Condorcet to be an artifact of the
system, or a representation of actual ambiguity, obviously plays a big
role here.

-wclark

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