[EM] Condorcet loser elimination PR
Chris Benham
chrisbenham at bigpond.com
Mon Jul 28 10:23:12 PDT 2003
James Green-Armytage wrote:
"Below is an illustrative example where, I think you will agree, your
revised method produces an unfair or counterintuitive result.
The election is between 5 candidates, for 3 seats.
There are 300 voters.
I will use a Hare quota, to keep things simple. (Yes, I know your method
specifies a Droop quota, but it doesn't matter for these purposes.)
The Hare quota is 300 / 3 = 100 votes.
The preference rankings are as follows:
86: A, B, C, D, E
15: B, A, C, D, E
100: C
15: D, E, C, B, A
84: E, D, C, B, A
I think that we can agree that the appropriate outcome is ACE, correct?
This is the outcome that plain STV gives, and it is the outcome that
CPO-STV gives.
Unfortunately, your revised method seems to produce an outcome of ABC."
James,
I seriously doubt your claim that using a Hare instead of a Droop quota "doesn't
matter for these purposes". I remember long ago getting it on good authority that
compared to the Droop quota, the Hare quota is correctly superceded rubbish. This
view has been recently confirmed by James Gilmour:
"When Hare and Droop are applied to transferable preferential voting (eg STV-PR),
the effect of the Hare quota to over-represent smaller groups can deny a larger
party its fair share of the seats to the extent that it gets fewer seats than a
smaller party with fewer votes."
In the case of your example, the Droop quota is 300/4 = 75. Since ACE each have
more than a Droop quota of first preference votes, then I and my proposed method
agree that ACE is the "appropiate outcome".
So I am afraid I don't understand your point.
Looking forward to your reply,
Chris Benham
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