--- On Thu, 22/1/09, Raph Frank <raph...@gmail.com> wrote: > Anyway maybe a non-manipulable method requires > > 1) a simple method to convert honest preferences into valid > votes > 2) this method may not use info about other voters > 3) If everyone else uses this method, then it is in your > interests to > also use this method > > One possible subjective aspect would be what simple means.
One could also drop the requirement of simplicity (since non-manipulability doesn't necessarily require that) and keep it as a separate requirement. > Methods that require some knowledge of polls to work would > fail this definition. "Non-manipulability" could also allow use of this knowledge. > However, most people have little problems with plurality > and use the > standard strategy quite effectively. > > I think the concept of requiring a zero-info strategy to be > optimal is > a clean way of saying that voters who have access to more > information > should not have an advantage (be able to manipulate). If there is a simple "non zero-info" strategy that all can easily use (as in Plurality) that could still be classified as "non-manipulable" (if otherwise ok). > Perhaps also, the zero info strategy should be reasonably > easy to understand. I already noted that simplicity could be a separate requirement / criterion. > The criterion could perhaps be relaxed a little by allowing > publicly > available information to be used rather than it being > purely zero-info Difficult to define what the public info is. But it would be good to have criteria that can be met more or less fully. > (and that the method is somewhat resistant to inaccuracies > in that > info). Also level of tolerance against inaccuracy, risk of backfiring of the strategy, required level and difficulty of coordination of the strategy, frequency of the vulnerability etc. would be good parameters. > Also, perhaps if the partial info strategy was only > 'slightly' > less effective than the optimal strategy under perfect > info, then that > would be OK too. Yes. I think too often we ignore the difference between failing some criterion in some rare cases and failing it regularly and in a way that allows strategic manipulation of the election. I try to summarize my comments in the form of some rough definitions. A "simple" method requires 1) a 'simple' method to convert honest preferences into optimal votes A "zero-info" method requires 2) this method may not use info about other voters, but still be able to convert honest preferences into optimal votes A "non-manipulable" method requires 3) it is in everyone's interests to use the default method to convert honest preferences into optimal votes (I didn't cover the "if everyone else uses this method" case.) These definitions allow also e.g. Approval to be categorized as (close to) "simple", not "zero-info" and "non-manipulable". One more definition to point out one weakness of Approval. A "decidable" method requires 1) a method to convert honest preferences into an unambiguous optimal vote The point is that the there should be no lotteries that may lead also to unoptimal votes but the best vote should be found in a deterministic way. Approval fails this criterion since picking the correct number of approved candidates is sometimes tricky (when there are more than two strong candidates). Juho ---- Election-Methods mailing list - see http://electorama.com/em for list info