Raph Frank wrote:
On Thu, Aug 21, 2008 at 7:23 PM, Kristofer Munsterhjelm
<[EMAIL PROTECTED]> wrote:
The decoy list strategy appears because it's possible to vote for a
different national party and regional party (constituency candidate), which
leads to an overhang that can be exploited to turn top-up into parallel MMP.
A simple countermeasure is to weight the vote pairs in a way that if you got
what you wanted in the constituency part, your say is diminished in the list
part.
This isn't possible though. Fundamentally, FPTP
means that a candidate can get 1 full seat while only
being supported by 1/2 a seat's worth of voters (and often
less).
Independents make it even worse (and as you say decoy
lists exploit this).
What I had in mind was something like this: Say there's a single-winner
election where the plurality winner has 35% support. Then those voters
effectively got 0.5 (+1) worth of the vote with only 0.35 mass. The
total voting power of the entire electorate should not be altered.
Thus
pA (unscaled) = 0.35/0.5 = 0.7
pB (unscaled) = 1.3
For the sake of the example, consider the case of 1000 votes. Then the
scaling factor is x, so that 0.7 * x * 350 + 1.3 * x * 650 = 1000. x is
then about 0.918, so the voters for the winner now have voting power
0.6426 and all the other voters have voting power 1.1934.
For a single seat election, STV would reduce to IRV. For 1000 ballots, the
Droop quota would be (1000/(1+1)) + 1 = 1000 * 0.5 + 1 = 501, which seems
right, considering a majority is 50% + 1.
It depends on how you want to look at it. If there are 100 seats,
then the quota is 1/101 of the votes cast. This works out as
100/101 of the votes cast in each constituency (assuming equal
turnout).
Thus unless a local candidate hit ~99% of the local vote, he
wouldn't actually reach the (national) STV quota.
That's true, so I don't think you should compress the entire election
into an STV election with the same quota. Instead, keep the weights
after the local election is done, and use those weights for the national
election.
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