[EM] ICT

[Michael Ossipoff]

Kristofer asked:

*What's the advantage of ICT over ICA? *
**
*[endquote]*

Kevin correctly answered:

* *I'm pretty sure Mike judges ICT to be defection-resistant while ICA
isn't.

[endquote]

Yes. A look at both methods in the Approval bad-example will show it. Let
me write that
example again:

Sincere rankings:

27: A>B
24: B>A
49: C

Actual ballots, when the A voters co-operate and the B voters defect:

27: A>B
24: B
49: C

Now, try ICT a ICA in that last set of rankings.

There is no equal top ranking, and so "unbeaten" means what we usually mean
by "not pair-beaten"..

ICT:

With the A voters' help, A beats C. With B voters defecting, C beats A. And
A beats B.

There are no unbeaten candidates. So we pick the candidate who is at 1st
rank on the most ballots.
That's C.

ICA:

Again, no one is unbeaten.

If ranking a candidate constitutes an approval, then B is the most approved
candidate. B wins, and the
B voters are rewarded for their defection.

And, even if we used separate Approval marking on the ballot, or an
Approval cutoff in the rankings,
the fact remains that if the A voters co-operate, by approving B, and the B
voters don't co-operate,
then B's defection succeeds.

ICT avoids that by disregarding the result of A's co-operation,when
choosing the winner, under these
conditions.

Kevin:

You continued:

Maybe predictably, I am a bit afraid of ICT because I don't think it's good
for voters to be
able to thwart another candidate's CW status, by ranking candidate Z over
him, without the
voter having to support Z in some sense during the cycle-breaker.

[endquote]

But, as Chris pointed out, the only candidate who can benefit from burial
strategy wouild be the
one with the most 1st choice marks in that strategic cycle. That greatly
limits the possibilities for burial strategy.

So the worst that can happen with burial strategy is the election of the
candidate with the most top-marks,
among the candidates in that artiricial cycle. We've certainly heard of
worse strategy problems than that.
All rank methods should have that as their strategy problem.

Mike Ossipoff



Kevin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20120423/4000a996/attachment-0003.htm>