[EM] Craig's dilemma example & IRV

[MIKE OSSIPOFF]

Craig mentioned an example where A & B voters have to decide whether
to trust eachother and vote for eachother's candidate, or to
take advantage of eachother by voting only for their own candidate.
A defection/co-operation dilemma.

I've just posted a message about the rarity of that scenario, but
I'd like to say something about IRV in those situations.

IRVies can proudly point to the fact that the A & B voters need only
rank sincerely. Their votes are sure to accumulate on an {A,B}
candidate, and that candidate will beat C.

This is related to IRV's compliance with Mutual Majority, and ICC.

But what the IRVies might not have noticed is what that situation means
to C voters. It might be difficult to care about them, because they've
been regarded as the enemy in the story, but, objectively, you don't
know which group you might belong to in some future election. For a
method to be free of a problem, it must be free of that problem for
every voter.

So what's your strategy situation as a C voter in IRV. The whole notion
of a dilemma among the {A,B} voters says that there's some significant
difference between A & B. Might you not like one better than the other
then? One of those will get eliminated and the other will win. If you
vote sincerely, with C in 1st place, your A>B or B>A preference will
never be counted, and you have no say in which wins. One thing for sure
is that you won't elect C. The only vote that strategically makes sense,
when it appears that C doesn't have a majority but that A + B adds up
to a majority, is for you to vote your favorite of A or B in 1st
place.

In other words, in the situation where IRV avoids that rare Approval
dilemma, that's an example where IRV strategically forces someone to
dump their favorite by voting someone else over him--something that
no one ever has any reason to do in Approval.

So much for IRV being better in that example.

Mike Ossipoff



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