Someone posted:
"Mono-add-top" is a Woodall criterion which says that adding ballots that all give
first-preference to X must not harm X. It is met by IRV and Margins, but not by WV.
I reply:
I'm not necessarily denying that, but can you demonstrate that those statements are correct?
Aside from that question, there are very many criteria, and all are failed by some methods.
It's been shown that all nonprobabilisitic methods can have incentive for strategy.
Predictably, different methods often have different strategy. Of those innumerable criteria, different methods meet different criteria.
Any criterion can be justified by someone saying "This criterion is important". In that way, there are a vast number of important critreria. A vast number of essential criteria, and no method meets them all.
When any one type of strategy incentive is looked at, it always looks undesirable, and a good-sounding argument can be made against whatever method has that strategy incentive. That's why you should keep in mind that no nonprobabilistic method is strategy-free. So it's a question of what kind of strategy incentive is worse.
No one can establish that one standad is more important than another. So, when asserting the importance of one's favorite standard, one is always safe from being contradicted.
Majority rule is a widely accepted standard. The lesser-of-2-evils problem is notorious. With only very few exceptions, nearly all single-winner reform advocates want to get rid of that problem. The goal of getting rid of the lesser-of-2-evils (LO2E) problem therefore is a widely held standard, as is majorilty rule.
It's been shown here that wv and, in some ways, Approval too, beats Margins and IRV by those 2 very widely-recognized standards.
Say a majority of the voters prefer X to Y. Y is a "greater-evil" whom they don't want to win. What must they do in order to keep Y from winning? With wv and Approval they'll never have to reverse a preference in order to keep Y from winning. Wilth IRV and Margins they'll sometimes have to bury their favorite, vote someone over their favorite if they want to keep Y from winning.
So methods like IRV and Margins illustrate that a shoddy rank-method is worse than not using a rank-method.
I might ask you what good it does to guarantee that voting your favorite in first place can't hurt your favorite, when you strategically need to bury your favorite.
That criterion, the Weak Defensive Strategy Criterion, is a modest, minimal thing that we'd expect of a method that honors majority rule and doesn't have the worst form of the lesser-of-2-evils problem.
As I mentioned in an earier message, there are, with Margins and IRV, situations (configurations of voters' preferences) in which the only Nash equilibria are ones in which some voters vote someone over their favorite in order to protect majority rule or to protect the win of a CW. But, with wv and Approval, every situation has at least one Nash equilibrium in which no one reverses a preference.
That's obviously a sense in which it can be accurately said that wv and Approval are sincere methods and that Margins and IRV are not.
By the way, about LNH, I've probably already said this here, but the reason why IRV doesn't let you lower preferences hurt your favorite is that IRV eliminates your favorite before it lets you help your lower choices. IRV saves your favorite from harm from lower preferences by eliminating your favorite before letting you help your lower preferences. A sort of electoral euthanasia.
Someone said that because IRV doesn't let lower preferences hurt higher ones, that means that IRV has no incentive for truncation. That isn't quite so. Saying that lower preferences can't hurt higher ones isn't quite the same as saying that adding more candidates to your ranking can't worsen the outcome for you. As I said before, Professor Steven Brams published an example refuting the claim that IRV never rewards truncation.
All four majority defensive strategy criteria measure for the popular standards of majority rule and getting rid of the lesser-of-2-evils problem.
Mike Ossipoff
_________________________________________________________________
Make your home warm and cozy this winter with tips from MSN House & Home. http://special.msn.com/home/warmhome.armx
---- Election-methods mailing list - see http://electorama.com/em for list info
