[EM] More 0-info pairwise strategy

[MIKE OSSIPOFF]

Blake spoke of how, if the goal is to make sure one or more
candidates don't win, then, with Margins, there's no incentive
to do other than sincerely rank the candidates whom one likes
more. But said that, with Condorcet, one would have incentive
to rank a number of candidates in 1st place.

Yes, if the goal is only to not elect that last choice.
Of course the whole reason why we'd like to not have to
equal rank candidates whom we unequally prefer is so that
we also often have reason to want to sincerely rank them.

And, in both Condorcet & Margins, there are reasons for
sincere ranking, and for ranking some candidates insincerely
at 1st place.

Of course defeating your last choice isn't really all that matters
to you usually, so in Condorcet, you have some reason to want
to sincerely rank the candidates whom Blake said you'd put
in 1st place. And in Margins, since defeating your last choice
isn't all you want, you'd like to protect your more preferred
candidates by sharing 1st place position with them. If you don't,
for instance, one of them could turn out to be a sincere CW who
lost because of truncation, and because you didn't insincerely
share 1st place with him.

So with both methods, there are reasons for both kinds of voting--
sincere ranking & 1st choice sharing. Your actual voting strategy
would be based on some calculation that would weigh the benefits
based on your utility assignments for the various candidates.

So how do the 2 methods differ? Find out after the election, when
the pairwise results are published. In Condorcet, if you voted
sincerely when you could have gained by sharing 1st place, then
you'll maybe regret that you didn't take advantage of some
fluke opportunity in a natural circualar tie. But in Margins,
if you voted sincerely when you would have gained by sharing
1st place, you can find that a sincere CW lost to truncation
because you didn't give support (by insincerely upranking him
to 1st place).

So the difference is--what do you want to regret? Not taking
advantage of a fluke win opportunity in a natural circular tie
with no right result? Or being part of a majority that has just
been had because you didn't adequately help the compromise that
you needed. That help is automatic in Condorcet when there's
no offensive order-reversal. Some consider help for a compromise
candidate whom you, in some majority group, have the power to
elect, to be especially important.

***

Another way of looking at it is to ask which method is more
Condorcet-efficient. A number of authors consider that an
important consideration. Even with 0-info, Condorcet's automatic
protection of sincere CWs against truncation seems to put it
in a whole different class from Margins in that regard.

Remember that only 2 things can keep a sincere CW from winning
in a pairwise method: Truncation or falsification of preferences.

***

I've noticed that some prefer "sincere CW" to mean what I
meant by "CW". And presumably many would use CW to mean what
I call "BeatsAll candidate". Ok, I'll use "sincere CW", and
maybe abbreviate it SCW. I'll still say BeatsAll candidate
to mean the candidate that beats each one of the others, unless
it's a sure thing that people prefer CW to have that meaning.
There's plenty of academic support for CW to mean sincere CW,
but I'll use SCW if that's preferred here.

Some authors say "Condorcet candidate" to mean SCW, so that
usage should be ok here too.

***

Mike Ossipoff

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