Thanks, Chris. I'll correct the errors and rephrase some things I didn't say correctly.
On the Compromise strategy, I think some compromises are more intuitive than others. I think it's intuitive to abandon a more weakly supported candidate, e.g. Nader, in favor of a major candidate, as is common in FPTP. But it strikes me as more counter-intuitive, at least for the average voter, to abandon a candidate with strong core support in favor of a more weakly supported candidate, as could happen under IRV. Then there's the issue as to whether the result of the strategizing is a better or worse result overall . . . but that's a tricky topic for another time. > Date: Thu, 20 Nov 2008 11:51:01 -0800 (PST) > From: Chris Benham <[EMAIL PROTECTED]> > Subject: [EM] Why I Prefer IRV to Condorcet > > Greg, > I generally liked your essay. I rate IRV as the best of the single-winner > methods that > meet Later-no-Harm, and a good method (and a vast improvement on FPP). > > But I think you made a couple of technical errors. > > "However, because bullet voting can help and never backfire against one's top > choice under > Condorcet, expect every campaign with a shot at winning to encourage its > supporters to > bullet vote. " > > Bullet voting can "backfire against one's top choice under Condorcet" because > Condorcet > methods, unlike IRV, fail Later-no-Help. > > http://groups.yahoo.com/group/election-methods-list/files/wood1996.pdf > > In this 1996 Douglas Woodall paper, see "Election 6" and the accompanying > discussion on > page 5/6 of the pdf (labelled on the paper as "Page 13"). > > Quoting again from your paper: > "As mentioned, every voting system is theoretically vulnerable to strategic > manipulation, and IRV > is no exception. However, under IRV, there is no strategy that can increase > the likelihood of > electing one's first choice beyond the opportunity offered by honest > rankings. While there are > strategies for increasing the chances of less preferred candidates under IRV, > like push-over, > they are counter-intuitive." > > The Push-over strategy is certainly not limited to improving the chance of > electing a "lower > [than first] choice". Say sincere is: > > 49: A? > 27: B>A > 24: C>B > > B is the IRV winner, but if? 4-21 (inclusive) of the A voters change to C or > C>? then the winner > changes to A. > > But as you say the strategy isn't "intuitive" , and backfires if too many of > the A supporters try it. > Some IRV opponents claim to like Top-Two Runoff, but that is more vulnerable > to Push-over > than IRV (because the strategists can support their sincere favourite in the > second round). > > The quite intuitive strategy that IRV is vulnerable to is Compromise, like > any other method that > meets Majority. But voters' incentive to compromise (vote one's front-runner > lesser-evil in first > place to reduce the chance of front-runner greater-evil winning) is generally > vastly vastly less > than it is under FPP. > > (There are methods that meet both Majority and Favourite Betrayal, and in > them compromisers > can harmlessly vote their sincere favourites in equal-first place.) > > But some Condorcet advocates are galled? by the Compromise incentive that can > exist where > there is a sincere CW who is not also a sincere Mutual Dominant Third winner. > > 49: A>B > 02: B>A > 22: B > 27: C>B > > On these votes B is the CW, but IRV elects A.? If the C>B voters change to B > then B will be > the voted majority favourite, so of course IRV like Condorcet methods and FPP > will elect B. > > Chris Benham ---- Election-Methods mailing list - see http://electorama.com/em for list info