[EM] SD & the defensive strategy criteria

[MIKE OSSIPOFF]

> > Say there are 3 candidates, and your favorite comes in "middle" in
> > the Approval count. Your favorite is B.
> >
> > B is sincere CW--is preferred to both A & C by more voters than 
>vice-versa.
> > A pairwise beats C.
> >
>
>If B is the sincere CW under Condorcet, then she will win in Approval
>Seeded SP, at least my version. Whether B starts in the middle or the
>bottom of the seeded list, she will win every pairwise comparison all of
>the way to the top.

Certainly, if B is the _voted_ CW. But B could be the sincere CW
without being the voted CW. If the A voters truncate, and don't
vote B over C, then they can allow C to beat B, even if B is sincere CW.
Then B is out of the election.

And if A voters actually order-reverse against B, voting C over B,
then likewise they can make C beat B, even if the C voters strategically
refuse to vote C over B. C voters, in order to save B, could then have
to vote B over C, in violation of WDSC & FBC.

Either way, it's then between A & C, and A beats C under sincere
voting (by assumption). I could write an example in which the B voters then 
can't prevent A from winning without insincerely voting C over A.


> > The Approval finishing order is
> > A, B, C. Some A voters truncate in the BC election. So, even though
> > B is sincere CW, B loses to C.
> >
> > When C goes agains A, A wins.
>
>In my version, A loses to B, so A stays at the bottom and is never
>compared to C.

But I'm saying the Approval finishing order is A, B, C. So the 1st
contest is between B & C. An example can be written in which truncation
or order-reversal by some A voters can allow or cause C to beat B, even
though B is sincere CW.

I admit that SFC, GSFC, FBC, & WDSC aren't criteria that you'll find in
journal articles, and so you might say that Approval-Seeded SD's
violation of those criteria isn't important. Not in the academic world.
But voters are very concerned about the lesser-of-2-evils problem, and
majority rule is a popular standard. I claim that the defensive strategy
criteria are the ones that best measure for both of those standards.

I should add the disclaimer that it's always possible that I don't
understand the method, or am making some other error. But it seems to
me that those criteria aren't met by that method.

Again, I admit that
those criteria aren't used in the academic world, but I claim that
they're about things that are important to voters.

In a meeting, when there's no computer, and a handraising vote is
desired, and there isn't time for any pairwise-count method,
then Sequential Pairwise isn't a bad solution, provided that people
are vigilant about order-reversal, and willing to retaliate against it
on a subsequent vote involving the reversers' alternative.  Approval
is a good way to seed SD. A quicker way is to write the alternatives on
the blackboard, in a vertical list, and flip a coin to decide whether to 
start from the top or the bottom of that list.

Myself, I'd much rather use Approval than SD in a meeting, however,
because Approval is such a good public elections proposal that I'd want to  
demonstrate Approval in the meeting.

Mike Ossipoff


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