[EM] Approval, IRV, FBC, Blake

[MIKE OSSIPOFF]

Forrest had written:

>
>When I pointed out all of the criterion that IRV failed (Monotonicity,
>Summability, Condorcet Criterion, FBC, etc.) the only one that concerned
>them was the FBC, but they felt that IRV satisfied it "well enough" and
>certainly better than Approval which lacked the expressivity that is
>necessary for the strong version of FBC that they consider essential: "It
>is never advantageous to rank another candidate as high as your favorite."
>

Blake replied:

I have some sympathy for their point. People certainly don't like
feeling compelled to vote someone over their favourite. But they also
don't like voting someone equal to their favourite. It seems to me that
you FBC-boosters greatly deride the first kind of strategy (even calling
it "betrayal") while being largely unconcerned with the second.

I reply:

Would Blake perhaps agree that one of those is worse than the other?
Burying one's favorite is worse than making him share 1st place.

Blake continues:

It
seems a lot of people don't feel that way. Maybe they are wrong, but I
hope we can end the constant claims that criteria like FBC reflect the
real desires of voters.

I reply:

Maybe Blake is a proponent of the stronger FBC. Would Blake like
to tell us about a method that meets that criterion? I doubt that
any 1-balloting method can meet it, though I'm not sure what the
merit-limits are when several ballotings are allowed. If there's
a method that meets Strong FBC, it surely would require a number
of ballotings, and probably complicated rules. Is there such a
method? If not, does it make any sense for Blake to say that
ordinary FBC isn't enough and that he wants more?
Forest had written:

>
>Some of them still believe that IRV completely satisfies this strong FBC. 
>Others believe that, although there are exceptions, they will hardly ever
>occur in practice. This despite my detailed diagrams, examples, etc. 
>showing how third party emergence dynamics almost inexorably lead to the
>stage where Favorite Betrayal is as inevitable as plurality's spoiler
>problem in the early stages of third party gestation. I pointed out that
>pregnancy tends to lead to the stage of labor.
>
Blake replied:

To put this in concrete terms, let's think about the Greens and the
Democrats. Eventually, in IRV, if the Greens get strong enough, once
they have more first choice support than the Democrats, they risk acting
as a spoiler. I suspect most Democratic IRV-enthusiasts don't believe
this will ever happen. They believe that the Greens will remain
marginal, but IRV will prevent them from acting as spoilers.

But, let's say that the Greens do eventually gain enough to become
spoilers in IRV. Have you noticed that a very similar thing happens in
Approval. The reason the Greens wouldn't be spoilers in approval is is
Greens all approve the Democratic candidate as well as the Green.
Otherwise they can be a spoiler. But the Greens can't possibly win an
election if they all vote for the Democrat. The Greens have to get a
lot of votes for them alone, to counteract those for the Democrat alone.
But as soon as this happens, there is a risk that the Republican will
win, and the Greens will regret their purely Green vote.

So, Approval has a very similar problem to IRV. I can certainly see why
Green supporters wouldn't see why IRV is much worse from this perspective.

I reply:

We'be been all over this subject here before. Yes, with both
methods the Greens could fail to help the Democrat when they need to,
and with both methods the Greens could mistakenly help the Democrat
when they don't need to, and give the election away to him. That
isn't really news.

As I've pointed out before, the difference there is that Approval
requires twice as many mistaken compromisers to give away the
election, as compared to IRV or Plurality.

Aside from that, the Greens who vote for Green & Democrat are
showing their support for the Green, while the Greens in IRV
who move Dem up to 1st place are dumping the Green and making it
look as if the Dem is their favorite.

If the Green could have beaten the Repub, and the Green ends up
with a higher vote total than the Repub, then the Greens will know
that next time they needn't vote for the Dem.

As I've said, Approval quickly homes in on the voter median, and
stays there.
>

Blake continued:

I must admit that I haven't been paying too much attention to the Five
Slot idea. Does five-slot pass FBC without being strategic ally
equivalent to approval? Or is it just that Five Slot is supposed to be
a simpler ballot than a normal rank ballot.


I reply:

Five-Slot is CR in which the voter can give to any candidate
an A, B, C, D, or F. It passes FBC.

Mike Ossipoff



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