On Jul 23, 2007, at 17:20 , Kevin Venzke wrote: > Juho, > > --- Juho <[EMAIL PROTECTED]> a écrit : >> Margins vs. winning votes is another long term discussion topic on >> this list. There have been many opinions and the final conclusions >> may be more difficult to draw than in the Range strategy question. > > I agree here. > >> 1) It can be debated if Condorcet methods are in practice (large >> scale public elections) vulnerable to strategies. If not, then both >> margins and winning votes are safe enough and other criteria can be >> used to pick one of them for use. > > It's possible that a coordinated strategy may not be feasible, but > that > is not the heart of the problem in my view. > > Referring again to this scenario: > 49 A > 24 B > 27 C>B > > Under margins the C voters have great favorite betrayal incentive > without > any other faction having to use a coordinated strategy.
Sorry about some delay in answering. There certainly are many viewpoints to this scenario. I'll present one. Please point out if I missed some essential things that you thought I should answer. In this example a single C supporter can indeed change the winner (in the case of margins) to B by voting B>C instead of C>B. The strategy is very safe since C supporters can assume that C will not win the race in any case. The pattern that leads to this strategic option is a loop where - A wins C clearly - C wins B with a small margin (and low number of winning votes) - B wins A with an even smaller margin (but high number of winning votes) How about the weak spots then: - The outcome is not that bad since there is anyway a majority that would elect B instead of A, and C was beaten too badly to even try to win (winning votes actually elect B without requiring strategic votes) - This scenario assumes a natural loop (not very common, and this type of loop maybe even less common than loops in general) - It is difficult to find a real world model that would lead to this kind of votes (what is the reason why voters voted as they did? do you have a story that would explain this election?) - Some of the strategic votes could be natural in the sense that if the numbers above are the outcome of an opinion poll few days before the election, then some C supporters might give up voting C as their first option since C seems to be "a sure loser" But of course the fact remains that in this scenario margins are more vulnerable to and encourage strategic voting. The weakest spot of this scenario is that it seems that it is not very likely to occur in real life. Maybe there are some variants with more credible "real life" numbers. This problem is margins specific but so far I couldn't find the reasons why this would make margins generally fail (worse and with higher probability than winning votes) in real life (large scale public) elections. I gave some links to the winning votes problems cases. They (for example) seemed more probable in real life to me than this scenario. But I have not done a complete enough analysis to claim that margins would definitely beat winning votes and that the probability of this scenario would be low enough not to be a threat. >> 2) There are as well cases where winning votes are more vulnerable to >> strategies than margins. So the question is not one-sided. > > However, it is pretty clear that margins has a worse FBC problem than > WV does. Simulations have shown this, but it can be argued > logically as > well. May be so. Is there some reason why FBC would be a key criterion in this case? I made some time ago some simulations on margins and winning votes on if some certain random voter group or any of the voter groups could (from their point of view) improve the outcome of the (sincere) election by voting strategically (in whatever way). The simulation gave margins somewhat better results than to winning votes. Maybe the results depend a bit on what one simulates. > If margins outperforms WV in some respect, I'd like to be able to > state > exactly how. - to me the choices that margins make with sincere votes seem (not necessarily perfect for all needs but) clearly more sensible than the choices of winning votes - some of the scenarios where winning votes have strategic problems appear to be more probable in real life than the problem scenarios of margins (this feeling is however based on only a limited number of cases and not a thorough analysis) - margins are easy to explain and understand and justify to the voters/citizens => "least number of additional votes needed to win all the other candidates" (no need to talk about breaking loops and about complex algorithms) Sorry about not providing any more exact answers. The first explanation above is very obvious to me. The second case is just an estimate. The third one is again a fact although "social and psychological" by nature. I've often seen some formal properties of voting methods presented as final proofs of the superiority/inferiority of some particular method. I don't measure the benefits as number of proven theorems. Especially in Condorcet methods the problem cases are typically related to scenarios that are not very common in real life. Therefore I'd like to see the claims linked to real world examples that demonstrate the theoretical scenarios in real life situations and estimate their probability, harmfulness, ease of applying them, risk of backfiring strategies etc. Juho > Kevin Venzke > > > > ______________________________________________________________________ > _______ > Ne gardez plus qu'une seule adresse mail ! Copiez vos mails vers > Yahoo! Mail > ---- > election-methods mailing list - see http://electorama.com/em for > list info ___________________________________________________________ All New Yahoo! Mail Tired of [EMAIL PROTECTED]@! come-ons? 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