[EM] Ree: IRV done right... satisfies Strong FBC?

Antonio Oneala watermark0n at yahoo.com
Tue Apr 4 14:13:37 PDT 2006

Kevin Venzke <stepjak at yahoo.fr> wrote: Hi,

Just passing through.

--- Antonio Oneala  a �crit�:
> This method seems to satisfy the Strong FBC, because your vote will not
> go to the second choice unless your candidate has absolutely no chance of
> winning.

To satisfy strong FBC, it would have to be the case that by changing your
vote from




you could not move the win from C to B, for example.

> It also passes the participation criterion, 

I have to disagree with this. Your showing up to vote can affect the
winners in an arbitrary way.

> It would satisfy the 
>  majority
>  criterion if you didn't allow people to rank as many people 1st place as
> they wanted, but I really don't see how limiting voter choice is going to
> improve the method too much.

You don't have to do that. Majority criterion usually refers to a
strict first preference.

>  From what I can tell from it, it ALMOST
> satisfies Arrow's Impossibility theorom, except that it is not fully
> deterministic because it makes a lot of assumptions about voter strategy.

I don't understand this. How do you satisfy Arrow's impossibility theorem?

This method is more like Bucklin than IRV. ER-Bucklin(whole) satisfies
weak FBC. I don't know of a deterministic method that satisfies strong FBC.

Kevin Venzke

You are correct on all of said points, and I now do realize that, as I said, I was doing some horrible math :) .  Bucklin would've been a better choice to compare it to, but I chose to diffrentiate it because votes are withdrawn.  IRV was a bad chioce to then compare it too, I'll admit.  In fact, an absolutely nonsensical one.

This actually seems to be one of the methods that a rash of people have come up with to try to satisfy a lot of criterion by voting strategically.  The thing I thought was "well, what would you want to do in an approval election"?  You want to vote for your favorite candidate, and not vote for the other candidates unless a less favorite candidate will be helped by doing so.

But this voting system doesn't resolve in any situation that can create a Condercet circular ambiguity:

85 A<C<B
75 C<B<A
80 B<A<C

In this example, they simply keep on throwing and withdrawing votes forever.

I personally don't think it is a Condercet method, because it is invulnerable to burying, and I don't see how a method could always pick the Condercet winner without being vulnerable to burying.  However, I've yet to throw an election at it that hasn't picked the Condercet winner, so maybe it does.  Because it is vulnerable to circular ambiguities, however, it at least needs a tiebreaker, which I have yet to come up with.  And there is probably a mess of criterion which I have missed.  So maybe this is a lemon...

Oh well.

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