On Dec 22, 2007, at 11:55 AM, Kevin Venzke wrote: > Jonathan, > > --- Jonathan Lundell <[EMAIL PROTECTED]> a écrit : >> On Dec 22, 2007, at 6:45 AM, James Gilmour wrote: >>> If you wish to utilise in some way all the information that could be >>> recorded on a preferential ballot, that is a completely >>> different voting system from IRV, with different objectives. The >>> preferences are no longer 'contingency choices', but take on a new >>> function depending on the detail of the voting system. It is almost >>> certain that the voters would mark their ballots in a different >>> way in an election by such a voting system from how they would mark >>> their contingency choices in an election by IRV. >> >> This seems plausible enough (and certainly IRV voters should be >> instructed along contingency lines). WRT marking ballots differently, >> setting manipulation aside, and considering only contingency vs >> preferential ranking, do you have an example or two of how and why a >> voter might end up with different ballots in the two contexts? > > I imagine James Gilmour is hinting at the fact that specifying lower > preferences under Condorcet methods can damage higher-ranked > candidates. So > the Condorcet voter has to think about how far down to rank while > the IRV > voter should not have to. > > Not just voter incentives but candidate incentives will vary by > method, > too. Clearly certain types of candidates will not be viable under > IRV but > could be under Condorcet. It would probably be more safe to give a > high > ranking to this sort of candidate under Condorcet than under IRV.
I can see that, more or less. STV and Condorcet are subject to different kinds of manipulation, and that could influence a voter's ranking. What I'm asking, though, is something else, and I concede in advance that it's a fuzzy question, or perhaps one with an obvious answer. Is there a case in which a voter's sincere ballot might differ between an IRV (contingent choice) election, and (say) a Condorcet-compliant election? I take James Gilmour to suggest that there might be, and while it seems plausible to me that there might, I'm not able to think of a clear example. It depends, I suppose, on what we mean by "sincere ballot", and here the literature is not very helpful; it relies on the intuitive idea that each voter has an ideal ranking of candidates, possibly with ties, possibly with don't-cares. It's easy to produce a counterexample for a multiple-seat STV election. Here the voter must deal with two different contingencies: my first choice might be eliminated, or my first choice might be elected with a surplus. My sincere second choice might well be different in those two cases; I might prefer A if only one of my top choices is elected, but prefer B and C if two are to be elected (let's say, for example, that B and C have complementary virtues, but that either alone might be less effective than A in representing my views). This problem doesn't arise in a single-seat STV (IRV/AV) election, of course. At the moment, my guess is that in fact the a difference arises only because of the different opportunities for manipulation presented by the different voting systems, but the question of whether a voter's sincere ranking might be different is intriguing. ---- Election-Methods mailing list - see http://electorama.com/em for list info
