On Fri, Feb 18, 2011 at 7:54 AM, Juho Laatu <[email protected]> wrote: > If you want to keep this property, the approach proposed by Michael Rouse > could determine > the number of board members. If most votes go to few candidates, then there > would be 5 members > (with different weight). If the votes are more distributed, then all > candidates (up to 9 candidates) > that get support over some agreed limit would be elected. Alternatively one > could use the number > of unrepresented votes as the criterion on how many members to elect. This > approach would > improve proportionality and keep the size of the board small at the same time.
You could still use PR-STV to give a proportional result. There is a formula which defines the "effective number of parties". It is also used in economics to define how many firms there are in a market. The formula is 1/sum((vote share squared)) So, if the first choice totals were A: 20% B: 30% C: 15% D: 12% E: 18% F: 5% The result gives: 1/(0.2*0.2 + 0.3*0.3 + 0.15*0.15 + 0.12*0.12 + 0.18*0.18 + 0.05*0.05) = 4.96 This says that there are around 5 groups in the vote, which is about right. If the voters were less concentrated, you get a larger number A: 8% B: 12% C: 7% D: 14% E: 6% F: 10% G: 9% H: 11% I: 4% K: 19% would give 8.56 The rule could be that you use that formula using the first choice votes and round to the nearest whole number between 5 and 9. Also, a property of the formula is that if the votes are exactly evenly distributed, then the number will be equal to the number of candidates. For example, if there were 8 candidates and each got exactly 1/8 of the vote, then the number of seats would be equal to 8. You can then use standard PR-STV with that number as the seats target. ---- Election-Methods mailing list - see http://electorama.com/em for list info
