OK, now on to the questions and responses on the other Criteria:
From: Jameson Quinn [mailto:[email protected]] Sent: Sunday, June 16, 2013 10:36 PM Subject: Re: [EM] Voting Criteria 101, Four Criteria In which case it (I think) becomes even more obvious and pointless as a criteria (as any system that gave the victory to people who get less votes, however we are counting and measuring votes, would make no sense, I think.) >>Name: Participation >>Description: If a ballot is added which prefers A to B, the addition of the ballot must not change the winner from A to B >>Thoughts: This seems to make sense. If we do not require this, then we permit voting systems where trying to vote sincerely >>harms your interests. Also, any voting system that would fail Participation would be I think fragile and react in not always >>predictable ways - like IRV. SO this seems to me to be a solid requirement, that I can't imagine a system that failed this >>Criterion to have some other benefit so wonderful to make failing Participation worth overlooking - I cannot imagine it. >You have fairly described the participation criterion. I would ask you to consider that this criterion focuses only on the >direction of preference, not its strength; and so it is inevitably biased towards preferential systems, and dooms you to live >within the limits set by Arrow's theorem. My two favorite systems - SODA voting and the as-yet-unnamed version of >Bucklin - both fail this criterion, though I would argue they do so in relatively rare and minor ways, and both satisfy some >weakened version of the criterion. I don't understand how a bias exists here. In every case I can currently imagine, if an election as it stands has A winning, and one more ballot is added which still prefers A to B, why should that ever cause the winner to change to B? Range/Score Voting: If A is winning, and the following ballot was added (A:90, B:89) A would still be winning. If IRV is being used and the following ballot is added (D first place, A second place, B third place) we wouldn't want B to suddenly be beating A. (Although in IRV I guess it could happen, but the point is that we wouldn't want it to, right?) This seems to be a serious issue. Whatever the voting method, if A is currently winning, and one more ballot gets added that happens to favor A with relation to B, how could it EVER be a good thing if B somehow becomes the winner through the addition of that ballot? I don't understand what bias has to do with the answer to that question? Also, how could Bucklin (as I understand it) *ever* fail this one? Because a ballot added that favors A to B under Bucklin would at minimum increase A by the same amount as B, possibly more, but would *never* increase B more than A, else the ballot could not be said to prefer A over B, right? OK, that's several questions. When would participation failure ever be a good thing? It wouldn't. But in voting theory, tradeoffs are common. A system which had other desirable features could fail a reasonable-sounding criterion, and if that failure is minor and/or rare enough, that could still be a good system. I'd argue that that's the case for Bucklin systems and the participation criterion. Though there are certainly many people here who would argue with me on that specific point, the fact is that choosing any system involves making tradeoffs. So, how does Bucklin fail participation? Imagine you had the following votes, giving candidates X and Y grades A-F 49: X:A Y:D 50: X:F Y:D The bloc of 50 voters is a majority, so they set the median. Or in Bucklin terms, Y reaches a majority at grade D, while X doesn't until grade F, so Y wins. Now add 2 votes with X:C Y:B. Now, X reaches a majority at grade B, while Y still doesn't until grade D. So now X wins, even though those votes favored the prior winner Y. I find this specific example implausible for multiple reasons, and think that actual cases of participation failure would be very rare. For instance, those last two voters could have voted X:F Y:B, and honestly expressed their preference without changing the result. OK, first of all, my brain does not seem to be able to handle letters on both sides of the colon (":"), so with your permission, let me alter the typography of your example, hopefully functionally changing nothing: 49: X:1st Y:4th 50: X:5th Y:4th So if I understand this right, under Bucklin, we look at all 1st place votes (we need at least 50), and see if we have over half - we don't, so now we look at all 2nd, still no, all 3rd, still no, and only when we consider 4th place do we finally have enough votes for candidate Y to have enough to win. Now we add two votes: 2: X:3rd Y:2nd Now we repeat the process, not enough 1st place votes (we need at least 51), not enough 2nd place votes, and adding in 3rd place we now have 51, precisely what we need for X to win. OK I think I see what you mean. That does show that with this system, adding in more ballots, even if those ballots prefer Y to X, can still change the outcome that would have been Y to X. I don't like that at all. It's moments like these that make me want to give up on even trying to pursue fair voting systems. Grrr.. I will think about this more, I really hate the idea that even theoretically it might be possible to add a ballot that prefers a candidate, and have that hurt the candidate. A lot. Also, as much as possible, for the sake of my brain, if you can avoid using letter grades in these examples, it will help me. Or I can simply try to translate like I did above to the best of my ability. >> IIA, on the other hand, strongly favors evaluative systems, because in comparative systems the entry of a new candidate >>can inevitably change the absolute ranking levels of existing candidates. I think that IIA is certainly a nice thing to pass, \ >>but I'd hesitate to make it a sine qua non. Independence of Irrelevant Alternative (IIA): Adding a new candidate B to an election that previously A would have won must not cause anyone apart from A or B to win. That is, if A would have won before B was added to the ballot, C must not win now. Again, I seem to be missing something here. If you are running an election with whatever method, and A would win, but then B enters the race, I can get A still winning. I can get B leaping ahead somehow and winning. What I cannot understand is how a candidate that A was beating before B's entry, somehow A now loses to. At least I cannot understand how any system that fails this criteria could still be worth considering - how the outcome of A beating C *until* B enters the race, after which C wins, is desirable. Is there some example that explain how this turn of events could be somehow fair or sensible? Again, it's a matter of tradeoffs. The systems I favor happen to meet IIA, but some people here think the Condorcet criterion, which is incompatible with IIA, is more important than it. Is it a well-established fact that Condorcet is incompatible with IIA? That you cannot have both? Independence of Clones: since you are saying that IoC is not equivalent with IIA, I will take up IoC independently along the way in a later set of criteria. I still am curious about this question: Question: it seems like the two above criteria - Participation and IIA - would be related. Is it possible to fail one and not the other? Or does either wind up mandating the other - for example, a system with IIA must also fulfill Participation, or vice versa? They are independent criteria. OK, then I will take up IoC separately and later. -Benn Grant eFix Computer Consulting <mailto:[email protected]> [email protected] 603.283.6601
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