[EM] Generalizing "manipulability"

[Raph Frank]

On Tue, Jan 20, 2009 at 10:57 AM, Kristofer Munsterhjelm
<km-elmet at broadpark.no> wrote:
> Perhaps. My point is not this. I explicitly said that I didn't know the zero
> info strategy ("not sure"). But also note that what I'm talking about is
> /zero info strategy/, i.e. how you'd vote if you were stuck on Mars with the
> candidates (who had broadcast systems with which to run their campaigns),
> and then you all traveled back to Earth just before the vote. The zero-info
> strategy may be something else than mean cutoff (again, *I don't know!*),
> but it may also just be lousy because the method has a bad zero-info
> strategy and voters have to know how others are likely to vote.

I wonder would zero info allow some knowlegde of the electorate.  (I
guess not :) ).

Not knowing anything about poll results, I think most voters could
split a set of candidates into "no hopers"/crazies and "possible
winners".  This would be based purely on the type of candidates who
were competitors in previous elections.

You could then use the mean strategy to determine the threshold, but
only include possible winners.

Anyway maybe a non-manipulable method requires

1) a simple method to convert honest preferences into valid votes
2) this method may not use info about other voters
3) If everyone else uses this method, then it is in your interests to
also use this method

One possible subjective aspect would be what simple means.

Methods that require some knowledge of polls to work would fail this definition.

However, most people have little problems with plurality and use the
standard strategy quite effectively.

I think the concept of requiring a zero-info strategy to be optimal is
a clean way of saying that voters who have access to more information
should not have an advantage (be able to manipulate).

Perhaps also, the zero info strategy should be reasonably easy to understand.

The criterion could perhaps be relaxed a little by allowing publicly
available information to be used rather than it being purely zero-info
(and that the method is somewhat resistant to inaccuracies in that
info).  Also, perhaps if the partial info strategy was only 'slightly'
less effective than the optimal strategy under perfect info, then that
would be OK too.