Another flaw in monotonicity

[Mike Ositoff]

> 
> On Mon, 2 Nov 1998, Blake Cretney wrote:
> 
> > If you really believe that not even 2nd preferences are meaningful, how
> > can you favor any method but plurality.  Except that that wouldn't
> > violate monotonicity.
> 
> Actually, Plurality does violate some forms of monotonicity in the
> necessity of voting for your "lesser of two evils" to avoid splitting your
> vote.

Plurlity does commit a violation very similar to nonmonotonicity,
but marginally less bad. Because, as David said, it can force
you to vote a less-liked alternative over your favorite, then
your participation in the election can produce a result worse
than would have happened if you'd stayed home instead of voting.

Any of the rank-methods proposed here can do that too. And in
the rank methods, even a sincere ranking can cause a worse result
for you than if you hadn't voted. Of course when Margins or IRO
forces you to vote something over your favorite, that makes it
even worse.

Approval is the method that doesn't do that. When proposing VA,
one tolerates that fault, because of VA's big strategic advantages.
But what's the reward for tolerating it with Margins or IRO? :-)

Ideally, if it could be attained, VA would be better than Approval,
I feel, because being able to always vote one's favorite over
everything else, for me, outweighs that violation of the
"Adverse Result" criterion. Margins & IRO have no such mitigating
advantage.

Mike



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