Re: [EM] RE : Ranked Preference benefits

[Chris Benham]

Juho, Juho wrote: On Nov 2, 2006, at 1:29 , Kevin Venzke wrote: Juho, --- Juho <[EMAIL PROTECTED]> a écrit : Example 1. Large party voters consider C better than the other large party candidate, but not much. 45: L>>C>R 40: R>>C>L 15: C>L=R Ranked Preferences elects L. (first round: L=-10, C=-70, R=-20; second round: L=-10, R=-20) In my opinion, if C is able to convince *every voter* to acknowledge that he is better than the major party alternative, then C is surely not a bad result. There is no need to convince every voter. This example is simplified (for readability) but not extreme since there could well be a mixture of different kind of votes. (See e.g. example 4.) The utility of C could be really low to the voters even though it was ranked higher than the worst candidate (in Range terms e.g. R=99, C=1, L=0). One of the key points of Ranked Preferences is that also weak preferences can be expressed and they may have impact. CB: So in your example is electing C a "bad result" or not?! As long as truncation is allowed, and voters have the opportunity to learn how the method works, I don't think "weak" CWs would be a real problem. I take this to mean support to basic (flat preference) Condorcet methods with active use of truncation. If they're not "good enough" to win at all, people should not be giving them votes. I'd prefer methods where voters can simply vote sincerely without considering when it is beneficial to truncate and when not. Yes, don't we all.  You like methods  that  meet  Later-no-Harm  and  Later-no-Help, so how then is your method supposed to be better than IRV? Condorcet voters need not leave non-approved candidates unlisted. I think Ranked Preferences provides some improvements. I'll try to explain. If A and B voters would all truncate we would end up in bullet voting and falling to a plurality style election. Not a good end result. 45: L>C=R 40: R>C=L 15: C>L=R Since it gives the same winner as your suggested method, why not? I think it is a problem of basic Condorcet methods that they easily elect the centrist candidate. No, that is their theoretical strength. One big (over-looked by you) reason why  the "weak, low-SU, centrist CW" is mostly a non-issue is that Condorcet methods create strong incentive for "strong" high-SU centrists to be nominated.  This idea is well explained in James Green-Armytage's July 2003 essay/post  "the responsiveness of  Condorcet". http://lists.electorama.com/pipermail/election-methods-electorama.com/2003-July/010083.html If preference strengths are not known electing the Condorcet winner is a good choice (and basic Condorcet methods are good methods). If preference strengths are known, then the choice is not that obvious. Ranked Preferences takes into account the relative strength of preferences (but not the "absolute strengths" in the Range style). The end result is more expressive than basic Condorcet but still quite immune to strategies (?). The "end result" is a horribly complicated, very awkward- to-operate monstrosity that we know fails both Condorcet and  *Majority Loser* ( but you hope is "quite immune to strategies".) I am a great fan of  "Definite Majority Choice" (DMC). http://wiki.electorama.com/wiki/DMC But suppose I was on the "same page" as you and thought that if  the CW is a "weak low-SU centrist"  then it is desirable to elect a  "higher-SU" candidate, and also that the "ranked preference" style of ballot you suggest should be used.  In that (hypothetical) case I suggest: "Interpreting ballots as approving all candidates above the strongest indicated preference gap ("ties" resolved by approving as many as possible without approving any ranked bottom or equal-bottom) calculate the Definite Majority set (i.e candidates not pairwise beaten by a more approved candidate). If  that set contains one candidate X only, elect X. If not eliminate (drop from the ballots and henceforth ignore) the candidate with the fewest top (among remaining candidates) preferences. (I prefer above bottom equal-ranking to be not allowed, but if it is, then "fractional"). Recalculate (among remaining candidates) the DM set and repeat the whole process until an X is elected." That at least meets  Majority Loser  and is relatively easy to operate. Also in common with IRV it meets Dominant Mutual Third, Majority for Solid Coalitions and  Condorcet Loser. 45: L>C>R 20: C>>R>L 35: R>>C>L In this example you give your method electing L, failing  Majority Loser. My suggested alternative (first) interprets the 45 L>C>R as L>C>>R and so calculates the initial DM set as {C} and so elects C. If instead the votes were 45: L>>C>R 20: C>>R>L 35: R>>C>L then all the candidates are in the initial DM set, so C is eliminated and then the "new DM set" is {R} so R wins. Example 4. Some of the large party voters think C is good but majority of them think C is no good. 15: L>C>>R 30: L>>C>R 14: R>C>>L 26: R>>C>L 15: C>L=R Initial approvals:  L45,  C44,  R40 C>R,  C>L,  L>R,  so initial DM set is {L,C}. Initial top preferences: L45,  R40,  C15. C is eliminated  and L wins  (agreeing with your method). Chris  Benham

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