Chris Benham wrote: > 38: A > 19: B>C>D > 17: B>D>C > 10: C>B > 03: C>D > 10: D>C > 03: D>B
My example here of DSC failing both DMT and Condorcet Loser works, but not quite what I meant to type: 38: A 19: B>C>D 17: B>D>C 10: C>D 03: C>B 10: D>C 03: D>B (I've "corrected" it below as well). Chris Benham > > Tim Hull wrote: > >> DSC uses a somewhat interesting method - it effectively goes and >> excludes the groups of candidates that the most people prefer a >> "solid coalition" to until it finds a winner. However, what I am >> wondering is - what are the primary flaws of these two methods >> (especially as compared with IRV, of which I know quite a bit about >> the flaws)? > > > DSC fails several important (in my book) criteria that are met by IRV. > > DSC fails "Dominant Mutual Third", which says that if there is a set > of candidates X that all pairwise beat all the outside-the-set > candidates and they are "solidly supported" > (ranked above all the outside-the-set candidates) on more than a third > of the ballots, then the winner must come from X. > > 49: A > 48: B > 03: C>B > > Here the DMT set is {B}, but DSC elects A. > > (If the B voters switch to B>C then B wins, a failure of > "Later-no-Help".) > > DSC fails "Condorcet Loser", which says that a candidate that is > pairwise beaten by every other candidate mustn't win > > 38: A > 19: B>C>D > 17: B>D>C > 10: C>D > 03: C>B > 10: D>C > 03: D>B > > DSC fails Condorcet Loser by electing A. > > This is also a failure of Dominant Mutual Third (DMT), by not > electing B. > > IRV is invulnerable to the Burying strategy. > > 49: A > 48: B>A > 03: C>B > > DSC elects A, but if the B>A voters change to B>C then their burial > strategy against A succeeds and B wins. > > DSC has a "random-fill" incentive and so fails what I call "No > Zero-Information Strategy". In the 0-info. case the DSC voter > gets a better expectation by strictly ranking all the candidates, if > necessary at random; whereas the IRV voter does best to > rank sincerely. > > I think of DSC as just FPP that has been minimally improved to meet > Clone-Winner and Majority for Solid Coalitions. > > Chris Benham > > > > ---- election-methods mailing list - see http://electorama.com/em for list info