Hi, De : Kristofer Munsterhjelm <[email protected]> >As a consequence, among ranked methods, some really bad methods (like >Plurality) >gets it wrong when there are two candidates plus no-hopes; some slightly >better >methods (like IRV, and perhaps I'd also put DAC/DSC here since it uses the >same >logic) can identify and remove the no-hopes but then gives bad results when >the >going gets tough; while yet other methods (such as Condorcet) use more >consistent >logic and, though not perfect, handle three-way (and n>3 n-way) races much >better.
I guess I might measure this as the need to compromise or compress, since this is what you probably do when the method won't handle the third candidate well. One figure I like to compute is the % of voters compromising plus half the % that compress. If I do that I get this for 1D scenarios: 17.1% FPP 16.3% Approval 9.2% DSC 7.9% TACC (the worst-scoring Condorcet method) 6.5% IRV 3.9% DAC 0.1% AWP explicit (the best-scoring Condorcet method) I can also look at the % of voters who feel the race was spoiled by one of the non-winning candidates (in a 3-candidate race): 12.0% FPP 2.2% Approval 2.1% DSC 0.98% Stensholt's BPW (the worst-scoring Condorcet method) 0.91% IRV 0.59% DAC 0.08% AWP explicit (the best-scoring Condorcet method) (There are some changes if I don't assume there is issue space. In particular, by the latter measure IRV and FPP see drastic improvement in relation to others.) >Rated method supporters, like Warren, would likely say that the rated methods >are >even better since they can pass IIA and so can scale to any number of >candidates. >They do pass IIA, but in exchange people have to be able to say how much they >like >a candidate rather than just better/worse-than, and it doesn't get around >Gibbard- >Satterthwaite. The voters also have to be willing to give a candidate the same score no matter which other candidates are in the race. So 10/10 can only go to the best possible candidates, 0/0 to the worst. If a 10/10 candidate enters the race, you can't demote a candidate to make room for the new one. If voters can't behave like this, then the IIA compliance doesn't amount to much. Kevin ---- Election-Methods mailing list - see http://electorama.com/em for list info
