Kristofer Munsterhjelm wrote:
The problem in using any other method than Plurality for counting the
votes in an STV method is that of elimination. If someone votes for A
with strength 1 and B with strength 0.5, and A wins, then how much do
you downweight that voter? The A voters should be reweighted so that
the surplus is distributed evenly, then A is eliminated, but if this
causes score changes, then the effective voting power is no longer
equal to the surplus.
I ran into that while trying to generalize STV to work with Borda (and
more generally, any sort of weighted positional system). Approval
without rescaling might dodge it (since the voting power doesn't
change by removing a candidate), but Range with rescaling wouldn't.
You could use Plurality (with vote-splitting between equally ranked
candidates) to determine surpluses and a different method to determine
eliminations. For example,
3 seats, Hare quota (100 votes)
100: Escher>Andre=Bush=Gore=Nader
110: Andre>Nader>Gore>Bush=Escher
18: Nader>Gore>Andre=Bush=Escher
21: Gore>Nader>Andre=Bush=Escher
6: Gore>Bush>Andre=Escher=Nader
45: Bush>Gore>Andre=Escher=Nader
After dealing with surpluses, we have:
28: Nader>Gore>Bush
21: Gore>Nader>Bush
6: Gore>Bush>Nader
45: Bush>Gore>Nader
Using Plurality for elimination would eliminate Gore. BUT if we instead
used the Borda count, the scores are:
Bush: 96
Gore: 127
Nader: 77
So *Nader* gets eliminated. In the final round, we have
Bush: 45
Gore: 55
So the winning set is {Andre, Escher, Gore}. Coincidentally, the same
as the CPO-STV result.
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