[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."

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compared to the Droop quota, the Hare quota is correctly superceded rubbish.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

More information about the Election-Methods mailing list