[EM] Re: Approval STV
fsimmons at pcc.edu
Mon Apr 5 14:43:02 PDT 2004
In this context (where Approval scores are used to eliminate candidates)
it might be better to use reverse weighted mean approval (RWMA).
To me it seems that RWMA would be best if relatively few candidates have
to be eliminated before someone gets a majority, and that regular WMA
would be better if most of the candidates have to be eliminated before one
gets a majority.
Maybe the reverse symmetric version that you once suggested would be the
best compromise for this context.
On Sat, 3 Apr 2004, Chris Benham wrote:
> You wrote (Wed.Mar.31):
> >A method I would rank between Condorcet and Approval is AER, or "Approval STV."
> >It's IRV, but the elimination order is based on approval. Because the approval
> >counts don't change, and the elimination order is thus fixed from the beginning,
> >it's monotonic. It's intuitive, and gives similar results to WV methods.
> To avoid the need for approval cutoffs, why not use the plain
> Weighted Mean Approval scores to set the
> fixed elimination schedule, and then the rest is like fractional IRV
> with a majority stopping rule ?
> Weighted Mean Approval .
> Voters rank the candidates, equal preferences ok.
> Each candidate is given a weight of 1 for each ballot on which that
> candidate is ranked alone in first place, 1/2 for each ballot on
> which that candidate is equal ranked first with one other candidate,
> 1/3 for each ballot on which that candidate is ranked equal first with
> two other candidates, and so on so that the total of all the weights
> equals the number of ballots.
> Then approval scores for each candidate is derived thus: each ballot
> approves all candidates that are ranked in first or equal first place
> (and does not approve all candidates that are ranked last or equal
> last). Subject to that, if the total weight of the approved candidates
> is less than half the total of number of ballots, then the candidate/s
> on the second preference-level are also approved, and the third, and so
> on; stopping as soon as the total weight of the approved candidates
> equals or exceeds half the total mumber of ballots.
> Chris Benham
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