[EM] percentage support - residual approval weights

Stephane Rouillon stephane.rouillon at sympatico.ca
Mon May 2 18:08:42 PDT 2005

I addressed this aspect some time ago on the (defunct)
yahoo list.  Some explanations are still alive in the EM archives.

Assuming, ranked ballot with an approval cut-off, like no ordering of
unacceptable candidates,
residual approval weights allow any ranking output result to be interpreted
as a percentage of the whole electorate.  This is obviously not a stable
(one simple vote change can have dramatic consequence on the percentages
distribution) but the result is an injection from each voter toward a unique
representative. I hope it is what you want.

Condorcet methods produce an order as output.
Reverse that output, eliminating the last candidate each time, just as in a
IRV election.
Every time the eliminated candidate was the last acceptable candidate of a
the residual approval vote of this voter goes to the eliminated candidate.
At the end every voter will have voted for only one candidate, the one most
wanted among its acceptable ones.

Pleased to be of any help,
Stephane Rouillon, ing.
PS: I think Forest built another alternative too.

Curt Siffert a écrit :

> I know many of us are here to work on the best method for various
> social choice purposes.  But many of us are specifically interested in
> political elections.
> And there's a problem with this.  Plurality actually serves two
> purposes.  It is a bad way to select a winner, but it is also a way to
> track percentage support over a period of time, and by determining
> proportional support when it's relevant.
> Democratic primaries are an example.  The proportion of votes a
> candidate receives determines how many delegates they receive.  But
> even if that particular decision structure is done away with, there are
> plenty of other reasons to track proportional support - polling, for
> instance.
> And this is something that Condorcet methods cannot do.  You cannot
> derive, from a Condorcet ballot collection, how much percentage support
> each candidate got.  You can't give each candidate a share of 100% in a
> way that all candidates would agree on.  If you can, I'd love to know
> how.
> Is this an already identified criteria?  The ability to determine
> percentage support?  The Siffert Criteria?  :-)  If so, Condorcet fails
> it; at least, I haven't seen a technique that would allow it to pass
> it.  What voting methods can convincingly a) identify the total
> available support (in terms of that vote method) for all candidates,
> and b) determine what percentage of that support each candidate
> received ?
> Thanks,
> Curt
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