[EM] vulnerability to compromise?

[MIKE OSSIPOFF]

>Blake Cretney introduced "burying" and "compromising" and
>claimed that he can measure the vulnerability. I asked him for
>further details but he didn't answer.

As I understand it, "burying" is what we've always here called
"offensive order-reversal". Though it's reasonable to speak of
vulnerability to an offensive strategy such as that, I don't
know what Blake means if he speaks of vulnerability to compromising.
But (rhetorical question) if compromising means insincerely
voting someone higher to make him win, then how could that be
considered something that shouldn't work, or something that
means that a method has a vulnerability fault if it works?

If "vulnerability to compromise" means that, with a method,
it can sometimes be necessary for a voter to insincerely vote
someone higher in order to prevent the election of someone worse,
then "vulnerability" seems the wrong word. I'd instead just say
that, with that method, compromise can be needed. It seems to me
that, with every method, it can sometimes be necessary for a voter
to insincerely vote someone higher in order to prevent the election
of someone worse. But with MDC (SDSC) complying methods it's
never necessary for a majority to do that. Methods that meet BC
meet MDC.

>
>You wrote (11 May 2000):
> > Markus' argument reminds me of Don Saari's argument that all
> > criteria failed by Borda, including manipulability, are failed
> > by other voting methods, so Borda is better because Borda
> > satisfies participation and reinforcement.

If Saari said or meant that all criteria failed by Borda are
failed by all other methods, that would be a very false claim.
If he meant that every criteria failed by Borda is failed by
at least one other method that wouldn't seem to mean much
except if Saari were trying to show that Borda isn't the worst
method because there's some method that doesn't dominate Borda
in regards to criteria. Actually, some of Borda's failings that
haven't been written as criteria could be. In any case, though,
Borda is the only method that I know of that can fail to elect
a candidate who is voted over all the others by a majority of all
the voters. It violates the Majority Criterion, sometimes called
the Majority Favorite Criterion.

>The MinMax method is a
>very good method because it meets Condorcet, Monotonicity,
>Positive Involvement and No Show. (Unfortunately, on the
>other side the MinMax method violates Local Independence
>from Irrelevant Alternatives, Independence from Clones and
>Reversal Symmetry.)

Also, that method, also known as Plain Condorcet, because it's
the literal interpretation of one of Condorcet's proposals,
meets SFC, but fails GSFC. It meets NDDC (WDSC), but fails
MDC (SDSC). Plain Condorcet's compliance with SFC is something that
sets it above all methods that aren't Condorcet versions.
It has the advantage of simplicity, but SD is nearly as simple
and meets GSFC & MDC. I claim that Plain Condorcet only fails
MDC under rare special conditions. Plain Condorcet's biggest
embarrassment must be its failure of Condorcet Loser and
Majority Loser, but I feel that those are only embarrassments
rather than practical reasons to reject the method. But
embarrassments can be harmful in an enaction campaign.

It seems to me that Plain Condorcet does slightly better at
adverse results criteria (criteria related to participation)
than the better Condorcet versions do, but their advantages
outweigh that.


Mike Ossipoff




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