On Sat, Jul 28, 2012 at 9:04 PM, Jameson Quinn <[email protected]> wrote:
> Is this [FBC7] essentially equivalent to the normal statement of FBC? It's roughly similar in strength, in the sense that the methods I know to pass one also pass the other. But it's not just another way of saying the same thing. The two criteria are different in significant ways. >Or is it > meaningfully stronger in some way? Yes, I think that it is. In one important way, FBC7 gives an important guarantee that the original FBC, known as Weak FBC, doesn't give. Weak FBC--even if the situation where that guarantee matters isn't being encountered. Weak FBC guarantees that, without voting someone over your favorite, you have _some_ way of getting as good a result as you could get by voting someone over your favorite. But, as someone pointed out: Maybe that way that doesn't need favorite-burial is a complicated and difficult-to-find strategy. That was what led me to look for a better FBC. With methods passing FBC7, you know that it isn't some mysterious unknown strategy that can get as good a result without favorite-burial. You know that adding additional candidates to 1st place isn't going to make any other 1st place candidates lose. Weak FBC is more vague in what it promises. With FBC7-passing methods, You cannot gain by favorite-burial. ...at least not by defeating a 1st choice. Of course, by raising Favorite to 1st place, you might make Favorite beat a Compromise whom you rank in 2nd place, who would have otherwise won instead of Worst. That isn't a Weak FBC failure, or a fault of FBC7, because you can avoid that by voting Compromise in 1st place too, and, if the method is ICT, you're then fully helping Compromise, in spite of Favorite being in 1st place too. If there's some set of candidates whom it's important to not elect, then you can rank everyone else in 1st place, in ICT. That's the u/a strategy in ICT--Rank all of the acceptables in 1st place. I suppose that (if the method isn't Double-Ended ICT) you might want to rank the unacceptables in reverse order of winnability, in order to maybe make a defeat for one of them. With Double-Ended iCT, there's no need to bother with that bottom-end strategy. It's considerably worse with ordinary (un-improved) Condorcet, with which you typically won't know what to do in a u/a election. Ranking all of the acceptables in 1st place creates a danger that you're letting one of them beat another, spoiling hir CW status and giving the win to an unacceptable. Approval and ICT have simple and easy u/a strategy--with Double-Ended ICT being more like Approval in that regard, because it doesn't have even the unacceptables-ranking strategy. Anyway, in comparison to Weak FBC, FBC7 compliance is easier to determine, and its guarantee is more concrete. Mike Ossipoff ---- Election-Methods mailing list - see http://electorama.com/em for list info
