John B. Hodges wrote: > CPO-STV is an awesome multiseat method, conceptually. I'm wondering > if there is a computationally efficient way of arriving at the same > "ideal" ensemble. My "For Dummies" guess is that the ideal ensemble > will never include a Condorcet loser and will always include a > Condorcet-winner if one exists. STV with Rob's "orphan" elimination > rule would (I guess) be sufficient to do that much.
I'm not sure I agree that the ideal ensemble should always include a Condorcet winner and exclude a Condorcet loser. For example, if we're electing two winners from three candidates and the preferences are 45:Reagan>Anderson>Carter 20:Anderson>Carter>Reagan 35:Carter>Anderson>Reagan I would argue that the outcome {Reagan, Carter} is the most proportionally representative. In a sense, the Reagan-first voters' preference for Anderson over Carter *should* be ignored since they already got their first choice in Reagan. (Would anyone disagree with that? Is there a good argument for preferring the outcome {Carter, Anderson}?) So this "ideal ensemble" includes the Condorcet loser (Reagan) and excludes the Condorcet winner (Anderson). The moral here is that single-winner and multiwinner elections are quite different. While the best single-winner methods can concentrate on limiting insincere voting without worrying about proportionality, the best multiwinner methods must strike a balance between striving for good proportionality and discouraging insincerity. I think of a spectrum with single-winner systems at one end and something like Direct Representation (http://www.directrep.org/) at the other. Strewn in the middle are n-winner systems. Somewhat paradoxically, "vote for any number of candidates" (Approval) is best for the single-winner case and "vote for only one candidate" (SNTV) becomes best for the n-winner case as n increases. Approval is great at removing insincerity from strategy but gives poor proportionality (which is irrelevant in the single-winner case), while SNTV often encourages insincerity (though less and less as n increases) but gives good proportionality (which improves as n increases). So it's not obvious to me that the best multiwinner systems reduce in the single-winner case to the best single-winner systems. ===== Rob LeGrand, psephologist [EMAIL PROTECTED] Citizens for Approval Voting http://www.approvalvoting.org/ __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com ---- Election-methods mailing list - see http://electorama.com/em for list info