[EM] full rankings, voter desire for

[Rob Lanphier]

Hi Kevin,

Thanks for the reply.

I'll have to think about some elements of your mail, but there are
pieces I want to respond to right away.

On Sun, 2005-10-16 at 05:55 +0200, Kevin Venzke wrote:
> --- Rob Lanphier <robla at robla.net> a écrit :
> > Here's a related set of questions I've been meaning to ask:
> > 
> > 1.  Are the Later No Harm (LNH) criterion and the Sincere Favorite
> > Criterion (SFC) mutually incompatible?
> 
> It seems I've caused some confusion. "Sincere Favorite" is my votes-only
> attempt at FBC. I don't know of any method which satisfies one of FBC and
> Sincere Favorite, but not the other, so there's not much need to discuss
> these criteria separately.
> 
> "SFC" stands for "Strategy-Free Criterion" as Mike said.

Oops, that was a thinko on my part when I was spelling out the
abbreviation.  I meant "Strategy-Free Criterion".

> > 3.  Are LNH, SFC and FBC mutually incompatible?
> > 
> > If the answer to #3 is "no", I'm very interested in figuring out a
> > system that satisfies those three.
> 
> As Mike said, MMPO satisfies all three of these (and Sincere Favorite).
> But it fails SDSC (and minimal defense) and Plurality.
[...]
>  Failing Plurality is
> probably not acceptable in a public election, since it makes the winner
> very hard to justify (i.e. you'd have to explain what positive incentives
> the method offers, to balance the counter-intuitive winner).

No argument here.   I'm assuming, though, that Plurality isn't mutually
exclusive of any of the other three (SFC, LNH, and FBC). 

> I don't believe SDSC and LNHarm to be compatible.


> When SDSC is failed, this means that the method can elect the wrong one of
> two frontrunners who have no overlapping support.

I'll have to think about this some more.

As a thought exercise for purposes of this conversation, and not really
as a serious proposal, I'd like to propose "Plurality-patched MMPO".
The procedure would be as follows:

1.  Eliminate all candidates whose selection would violate the Plurality
criterion
2.  Determine the MMPO winner from the remaining candidates.

I'm going to play around with this myself, and try to understand its
properties and differences to plain MMPO.  If something immediately
obvious that's bad about this strikes you, let me know.

A simpler variant of this would be "Majority ranked MMPO":
1.  Eliminate all candidates who aren't ranked on a majority of ballots
2.  Determine the MMPO winner from the remaining candidates.

I imagine that this filter causes a LNHarm failure, but I think it also
points to a slightly weaker variant of LNHarm that may be more useful
than pure LNHarm.

Rob