CR & Arrow

Forest Simmons fsimmons at
Mon Oct 21 17:02:28 PDT 2002

On Sun, 20 Oct 2002, Alex Small wrote:

> >
> > Of course that depends on how one defines IIAC. By the simple way that
> > I define it, Approval & CR comply.  But people have told me that they
> > believe that IIAC means something other than what I say it
> > means. But no one who has told me that has supplied a complete &
> > precise definition of what he thinks IIAC means.
> I ran across a paper (can't remember the journal, but it was recent) by
> a mathematician at Northwestern.  He defined IIAC to account for
> strategy changes:  If a candidate is deleted, and voters change their
> strategies to account for that, the outcome should be unchanged unless
> the deleted candidate was the original winner.
> Using the maximum-utility strategy causes Approval to flunk this
> criterion.  If you vote for all candidates whom you find superior to an
> expected utility, deleting a candidate changes the expected utility of
> the race, which causes you to change strategies, which can change the
> outcome.
> I wasn't terribly impressed.  First, this definition of IIAC isn't all
> that useful (any election method flunks it, as far as I can tell).

Any method that satisfies majority rule when restricted to two candidates
fails this version of the IIAC.


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