Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Juho wrote: Many of the criteria would be nice to have. One must however remember that often they have two sides. Winning something in some area may mean losing something in another area (e.g. the LNH property of IRV has been discussed widely on this list recently) especially when trying to fix the last remaining problems of the Condorcet methods. And if one assumes that strategic voting will not be meaningful in the planned elections then one should pay attention also to performance with sincere votes, not only to the resistance against strategies. Different elections may also have different requirements, so the question of which one of the methods is best may depend also on what kind of winner one wants to get (e.g. in some cases the best winner could be found outside the Smith set). That's true. Some of the criteria are mutually exclusive, yet others are not. By picking criteria of worth, one might build a Pareto front: those methods on the front are those that fulfill as many criteria as possible subject to that some are mutually exclusive. If we didn't forget notable criteria (and thus exclude from the Pareto front methods that by all means should be there), then the front provides the best methods we can get. It's up to one's judgement which of the criteria count more, i.e. which method on the Pareto front one should pick. For convenience's sake, I've ignored the problem that criterion compliance might degrade the method's goodness when given honest votes, and that we don't know which criteria are mutually exclusive. For the former, we (E-M members) disagree about how to go about measuring how good results a method provides on honest votes, and for the latter, we can still build a Pareto front based on the methods we know so far - but it might be incomplete. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Kathy Dopp wrote: Thanks Kristofer for the explanations. Do you know a good place that discusses the Ranked Pairs method of resolving cycles, or all the methods of resolving cycles? I would still like an example of a spoiler in Condorcet no matter how unlikely if possible. Thank you. Wikipedia explains Ranked Pairs well enough: http://en.wikipedia.org/wiki/Ranked_Pairs It doesn't explain River, because that method is less known. In both Ranked Pairs and River, you first sort the majorities (A beats B) by magnitude, greatest first. In Ranked Pairs, you then go down the list, locking majorities except those that lead to a contradiction with what you've already locked (e.g. if you lock A beats B and B beats C, you can't lock C beats A), and at the end you have an ordering, and the candidate at the top of this ordering is the winner. In River, you do the same, except that you're also forbidden from locking a victory against someone who has already had a victory locked against him (e.g. A beats B, then you can't lock C beats B). The root of the tree diagram (base of the river) is the winner. As for a spoiler in your terms, consider this very simple election (showing the Condorcet paradox): 10: ABC 10: BCA 11: CAB If the method picks A, then B is a spoiler for C, because removing B leads C to win: 21: CA 10: AC If the method picks B, then C is a spoiler for A, because removing C leads A to win: 21: AB 10: BA If the method picks C, then A is a spoiler for B, because removing A leads B to win: 20: BC 11: CB. That should work for any election method that reduces to a majority vote when there are only two candidates, because, as I've shown, it doesn't matter which candidate is elected - you can still show there's a spoiler. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Juho wrote: On Jan 22, 2010, at 12:05 AM, Kristofer Munsterhjelm wrote: Jonathan Lundell wrote: In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? A very abstract concept of spoiler might be: denote f(X) the minimal number of ballot changes/additions required to make X the winner. Then a spoiler is a candidate with a high f-value relative to the number of ballots (thus hard to get to win), who, by his presence, still changes who wins. Determining f(x) for the various candidates would be very hard, though, and one also runs into the question of what threshold to say above this f-value, spoiler, below it, not a spoiler. Maybe one should add also the requirement that the spoiler makes the result worse from spoiler's or spoiler's supporters' point of view. Yes, although that cannot be mechanically tested. For some very strange methods, it might be true that adding a candidate changes the winner to someone who everybody who voted for the winner ranked ahead of him, but that would be a very strange method indeed. Another possible modification is not to require f(X) to be high. One would just see what would have happened with and without the spoiler. According to that definition also strong candidates (but not actual winners) could be spoilers. (Typically term spoiler refers to minor candidates since these discussions typically refer to a two-party set-up, but the corresponding scientific term might or might not be limited to minor candidates and/or this particular set-up.) Then a spoiler is just a candidate whose presence shows IIA failure, subject to that this IIA failure must happen in first place (the winner changes, not lower in the ranking). The definition of IIA implies that the candidate (spoiler) can't be the winner. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 23, 2010, at 1:55 PM, Kristofer Munsterhjelm wrote: Juho wrote: On Jan 22, 2010, at 12:05 AM, Kristofer Munsterhjelm wrote: Jonathan Lundell wrote: In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? A very abstract concept of spoiler might be: denote f(X) the minimal number of ballot changes/additions required to make X the winner. Then a spoiler is a candidate with a high f-value relative to the number of ballots (thus hard to get to win), who, by his presence, still changes who wins. Determining f(x) for the various candidates would be very hard, though, and one also runs into the question of what threshold to say above this f-value, spoiler, below it, not a spoiler. Maybe one should add also the requirement that the spoiler makes the result worse from spoiler's or spoiler's supporters' point of view. Yes, although that cannot be mechanically tested. For some very strange methods, it might be true that adding a candidate changes the winner to someone who everybody who voted for the winner ranked ahead of him, but that would be a very strange method indeed. Yes. And there are also situations where some of the supporters of the spoiler are happy with the changes but some are not. A theoretical definition of the spoiler property might require all supporters to be unhappy (if simpler that way). I was thinking also about methods like Borda where in 60: AB, 40: BA A wins but addition of B2 (= 60: ABB2, 40: BB2A) means that B wins. B2 in a way spoils the election in general (and from A point of view) but from B point of view B2 saves the election. B and B2 are maybe from the same party but B2 is just worse. The B party may make the decision on if B2 will be nominated as a candidate (not the A party (that would spoil the election from their point of view if they did so)). Another possible modification is not to require f(X) to be high. One would just see what would have happened with and without the spoiler. According to that definition also strong candidates (but not actual winners) could be spoilers. (Typically term spoiler refers to minor candidates since these discussions typically refer to a two-party set-up, but the corresponding scientific term might or might not be limited to minor candidates and/or this particular set-up.) Then a spoiler is just a candidate whose presence shows IIA failure, subject to that this IIA failure must happen in first place (the winner changes, not lower in the ranking). The definition of IIA implies that the candidate (spoiler) can't be the winner. ...plus the spoiling (not just changing) requirement. Juho Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 21, 2010, at 9:29 AM, Kristofer Munsterhjelm wrote: robert bristow-johnson wrote: i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. Most Condorcet related problems occur only when there is no Condorcet winner (i.e. there is a top level cycle in the group preferences). Sincere or artificially generated cycles are the root cause of both problems with sincere votes (e.g. spoiler related problems) and strategic voting related problems in Condorcet. Different Condorcet methods (e.g. Ranked Pairs, Schiulze) are quite similar in the sense that the basic vulnerabilities of Condorcet methods exist in all of them (e.g. the basic burial scenarios). Their differences between the most common Condorcet methods are quite small in the sense that in real life elections they almost always elect the same candidate. Their differences are mostly related to how well they can resist strategic voting. Another point of view is to compare which method elects the best/correct winner with sincere votes. What is good in all the common Condorcet methods is that their vulnerabilities to strategies (and their differences in general) may very well be so small in typical real elections (large, public, with independent voter decision making, with changing opinions and less than perfect poll information) that strategic voting will not be a problem. Also their differences with sincere votes (e.g. spoiler related problems) are quite small in real life elections. Here's one simple spoiler related example as a response to Kathy Dopp's request. 35: ABC 33: BCA 32: CAB I this example there are three candidates in a top level cycle. If any of the candidates would not run that would mean that there is a Condorcet winner, and that winner would be different in each case. Let's say that the method we use will pick A as the winner. If B would not run then the votes would be 35: AC, 33: CA, 32: CA and C would win. B is thus a spoiler from C's point of view. I note however that these spoiler cases in Condorcet are not as common as in many of the other methods. In practice it may be that there is no need to worry about these cases. Maybe Kathy Dopp's comparisons will reveal something about how problematic the spoiler effect is or is not in Condorcet. Not also that in the example above B was not a minor party candidate (often term spoiler refers to minor candidates) but a pretty strong candidate. MAM/Ranked Pairs is also pretty strategy-resistant and is easier to understand. Schulze has the advantage of producing better results in some cases (closer to Minmax), but if ability to describe to the public is important, then Ranked Pairs wins there. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? (...) i would say that (with the CW existing), it's spoiler-proof. Yes. If there's a CW and a candidate is added, and that candidate doesn't create a cycle, then the winner doesn't change. All the tricky stuff happens when there is a cycle, or the candidate makes one. The advanced methods can claim further resistance: Schulze and Ranked Pairs both make their winner decision independent of candidates not in the Smith set. River is independent of Pareto- dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say YX, and there's at least one such voter). I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work). Yes, in small elections (with few voters only) it may be possible to know the opinions of each voter and agree about the applied strategy with the strategizing voters. In typical large real life elections many of the vulnerabilities are not practical and sincere voting may be the best strategy to most if not all voters. Many of the criteria would be nice to have. One must however remember that often they have two sides. Winning something in some area may mean losing something in another area (e.g. the LNH property of IRV has been discussed widely on this list recently) especially when trying to fix the last remaining problems of the Condorcet methods. And if one assumes that strategic voting will not be meaningful in the planned
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Thanks Kristofer for the explanations. Do you know a good place that discusses the Ranked Pairs method of resolving cycles, or all the methods of resolving cycles? I would still like an example of a spoiler in Condorcet no matter how unlikely if possible. Thank you. Kathy On Thu, Jan 21, 2010 at 2:29 AM, Kristofer Munsterhjelm km-el...@broadpark.no wrote: robert bristow-johnson wrote: i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. MAM/Ranked Pairs is also pretty strategy-resistant and is easier to understand. Schulze has the advantage of producing better results in some cases (closer to Minmax), but if ability to describe to the public is important, then Ranked Pairs wins there. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? (...) i would say that (with the CW existing), it's spoiler-proof. Yes. If there's a CW and a candidate is added, and that candidate doesn't create a cycle, then the winner doesn't change. All the tricky stuff happens when there is a cycle, or the candidate makes one. The advanced methods can claim further resistance: Schulze and Ranked Pairs both make their winner decision independent of candidates not in the Smith set. River is independent of Pareto-dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say YX, and there's at least one such voter). I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work). -- Kathy Dopp Town of Colonie, NY 12304 phone 518-952-4030 cell 518-505-0220 http://utahcountvotes.org http://electionmathematics.org http://kathydopp.com/serendipity/ Realities Mar Instant Runoff Voting http://electionmathematics.org/ucvAnalysis/US/RCV-IRV/InstantRunoffVotingFlaws.pdf Voters Have Reason to Worry http://utahcountvotes.org/UT/UtahCountVotes-ThadHall-Response.pdf Checking election outcome accuracy --- Post-election audit sampling http://electionmathematics.org/em-audits/US/PEAuditSamplingMethods.pdf Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 21, 2010, at 1:03 AM, Juho wrote: What is good in all the common Condorcet methods is that their vulnerabilities to strategies (and their differences in general) may very well be so small in typical real elections (large, public, with independent voter decision making, with changing opinions and less than perfect poll information) that strategic voting will not be a problem. Also their differences with sincere votes (e.g. spoiler related problems) are quite small in real life elections. Here's one simple spoiler related example as a response to Kathy Dopp's request. 35: ABC 33: BCA 32: CAB I this example there are three candidates in a top level cycle. If any of the candidates would not run that would mean that there is a Condorcet winner, and that winner would be different in each case. Let's say that the method we use will pick A as the winner. If B would not run then the votes would be 35: AC, 33: CA, 32: CA and C would win. B is thus a spoiler from C's point of view. I note however that these spoiler cases in Condorcet are not as common as in many of the other methods. In practice it may be that there is no need to worry about these cases. Maybe Kathy Dopp's comparisons will reveal something about how problematic the spoiler effect is or is not in Condorcet. Not also that in the example above B was not a minor party candidate (often term spoiler refers to minor candidates) but a pretty strong candidate. In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
well, since no one else responded... On Jan 21, 2010, at 9:21 AM, Kathy Dopp wrote: Thanks Kristofer for the explanations. Do you know a good place that discusses the Ranked Pairs method of resolving cycles, or all the methods of resolving cycles? Wikipedia. maybe start with http://en.wikipedia.org/wiki/ Voting_systems and see what you find from there. I would still like an example of a spoiler in Condorcet no matter how unlikely if possible. the spoiler would have to either push a nicely resolved election with a CW into a cycle and have the cycle resolved so that the earlier CW does not win or, if the election was in a cycle in the first place (but resolved to pick some winner), the spoiler would have to cause the election algorithm to choose a different winner (and not the spoiler). -- r b-j r...@audioimagination.com Imagination is more important than knowledge. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
robert bristow-johnson wrote: so, we have a CW... add a candidate, if that candidate does not become the winner, nor cause a cycle, then the Condorcet Winner we had before continues to be the CW with the added candidate. (boy, i guess we're rephrasing the same thing multiple times!) Yup. River is independent of Pareto-dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say YX, and there's at least one such voter). i wouldn't mind if someone explains this. i don't know what Pareto-dominated is about. can someone expound? A is Pareto-dominated by B if all voters who express any difference in preference between A and B, prefer B to A. Note that a voter may simply leave both unranked - that wouldn't count towards either's Pareto dominance. If all voters equal-rank B and A, that doesn't count towards any Pareto-dominance, either. A is Pareto-dominated (period) if there's some other candidate by which it is Pareto-dominated. The strong Pareto criterion states that Pareto-dominated candidates shouldn't win. This makes sense, because say X won and was Pareto-dominated. Then people could (rightly) complain that everybody who expressed some preference between X and some other candidate Y, preferred Y, and therefore Y should have won. Independence from Pareto-dominated alternatives then simply means that Pareto-dominated candidates can't be spoilers either - they can't even change who wins. I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work). yes, that's the whole point. this is why i am not yet afraid of someone strategically voting to push a Condorcet election into a cycle. it would be an unsafe way to accomplish a political goal. how could anyone predict what would happen? A party might still try, thinking they could pull it off; but complying with a strategic criterion stops that dead, because there's no way it's going to work. It doesn't even have to entertain the thought of trying. With advanced methods, the barrier imposed by these criteria might be so steep that the only remaining strategies are those where a sizable fraction of the electorate has to cooperate, and then it's practically strategy-proof in large public elections (barring disorganized strategy like the a sizable fraction goes on a Burial spree because each individual voter thinks they have nothing to lose of Warren's DH3). Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Jonathan Lundell wrote: In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? A very abstract concept of spoiler might be: denote f(X) the minimal number of ballot changes/additions required to make X the winner. Then a spoiler is a candidate with a high f-value relative to the number of ballots (thus hard to get to win), who, by his presence, still changes who wins. Determining f(x) for the various candidates would be very hard, though, and one also runs into the question of what threshold to say above this f-value, spoiler, below it, not a spoiler. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 21, 2010, at 5:33 PM, Jonathan Lundell wrote: On Jan 21, 2010, at 1:03 AM, Juho wrote: What is good in all the common Condorcet methods is that their vulnerabilities to strategies (and their differences in general) may very well be so small in typical real elections (large, public, with independent voter decision making, with changing opinions and less than perfect poll information) that strategic voting will not be a problem. Also their differences with sincere votes (e.g. spoiler related problems) are quite small in real life elections. Here's one simple spoiler related example as a response to Kathy Dopp's request. 35: ABC 33: BCA 32: CAB I this example there are three candidates in a top level cycle. If any of the candidates would not run that would mean that there is a Condorcet winner, and that winner would be different in each case. Let's say that the method we use will pick A as the winner. If B would not run then the votes would be 35: AC, 33: CA, 32: CA and C would win. B is thus a spoiler from C's point of view. I note however that these spoiler cases in Condorcet are not as common as in many of the other methods. In practice it may be that there is no need to worry about these cases. Maybe Kathy Dopp's comparisons will reveal something about how problematic the spoiler effect is or is not in Condorcet. Not also that in the example above B was not a minor party candidate (often term spoiler refers to minor candidates) but a pretty strong candidate. In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? In Plurality a typical spoiler scenario is one where the spoiler is a minor candidate (e.g. Nader in the US presidential elections). In IRV the spoilers are typically stronger. Here's one IRV example where the centrist candidate (C) wins. 30: RCL 35: CLR 35: LCR Then we add one more candidate (C2, spoiler) that the R and L supporters strongly dislike. 30: RCLC2 15: CC2LR 20: C2CLR 35: LCRC2 As a result C will be eliminated first, R next, and since C2 is not a strong candidate L will win. C2 thus was a spoiler from C's point of view. C2 is not fully a minor candidate. Although C2 has no chances to win C2 has more first preference votes than C. In IRV this kind of chains of influence could be also longer (5 candidates, 6 candidates etc.), and as a result the spoilers could be more and more minor. But on the other hand the probability of such minor candidates spoiling the election is very low. So, in theory also very minor spoilers are possible but they don't seem probable in practice. This is related to the observation that while Plurality may be in trouble already when there are only two major candidates, main problems of IRV (and Approval and Range) seem to appear only when there are at least three credible candidates. Juho Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 22, 2010, at 12:05 AM, Kristofer Munsterhjelm wrote: Jonathan Lundell wrote: In that case it might be a good starting point to define spoiler, so we know what we've found when we find it. What's an example of an IRV spoiler who's not a pretty strong candidate? A very abstract concept of spoiler might be: denote f(X) the minimal number of ballot changes/additions required to make X the winner. Then a spoiler is a candidate with a high f-value relative to the number of ballots (thus hard to get to win), who, by his presence, still changes who wins. Determining f(x) for the various candidates would be very hard, though, and one also runs into the question of what threshold to say above this f-value, spoiler, below it, not a spoiler. Maybe one should add also the requirement that the spoiler makes the result worse from spoiler's or spoiler's supporters' point of view. Another possible modification is not to require f(X) to be high. One would just see what would have happened with and without the spoiler. According to that definition also strong candidates (but not actual winners) could be spoilers. (Typically term spoiler refers to minor candidates since these discussions typically refer to a two-party set- up, but the corresponding scientific term might or might not be limited to minor candidates and/or this particular set-up.) Juho Election-Methods mailing list - see http://electorama.com/em for list info
[EM] I need an example of Condorcet method being subjected to the spoiler effect if any
If the Condorcet method is susceptible to the phenomena of a nonwinning candidate whose presence in the election changes who would otherwise win the election, all else being equal. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? Thanks. I'm devising an experiment to compare the Condorcet method with the IRV method of counting rank choice ballots and would like, if possible, to introduce subjects to the spoiler effect to see under what conditions they notice it occurs. I can easily generate spoiler scenarios with IRV but do not know how to generate spoiler scenarios with the Condorcet method and if it's not too much trouble, would appreciate an example if Condorcet is susceptible to spoilers. Thank you. -- Kathy Dopp Town of Colonie, NY 12304 phone 518-952-4030 cell 518-505-0220 http://utahcountvotes.org http://electionmathematics.org http://kathydopp.com/serendipity/ Realities Mar Instant Runoff Voting http://electionmathematics.org/ucvAnalysis/US/RCV-IRV/InstantRunoffVotingFlaws.pdf Voters Have Reason to Worry http://utahcountvotes.org/UT/UtahCountVotes-ThadHall-Response.pdf Checking election outcome accuracy --- Post-election audit sampling http://electionmathematics.org/em-audits/US/PEAuditSamplingMethods.pdf Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 20, 2010, at 7:10 PM, Kathy Dopp wrote: Is the Condorcet method susceptible to the phenomena of a nonwinning candidate whose presence in the election changes who would otherwise win the election, all else being equal? i changed the sentence form into a question. i hope that was okay, Kathy. don't wanna misquote anyone. i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? in the ranked-order ballot, no matter what their absolute ranks are, if A is ranked above B (or A is ranked while B is not), that counts as a vote for A. likewise for B ranked above A. doesn't matter if they were ranked 4th and 5th. just like the IRV final round between A and B, Condorcet will total how many votes with AB and compare that to votes where BA. whether C is in the race or not, for each individual ballot, if AB with C on the ballot, A would continue to be ranked above B (whether C is higher than either, in between, or below either). with the meaning of every ballot, regarding A and B, unchanged (whether C is there or not), the vote counts for AB and BA do not change. so every Condorcet tally not involving candidate C will remain unchanged, the tallies involving C are not there if C is removed. if A (or whoever is not C) was the Condorcet winner before C was removed, then the AX tally exceeds XA for any X. then A would continue to be ranked over all of the other remaining candidates with the same tallies as before even with C removed, because every tally not involving C would remain unchanged. i would say that (with the CW existing), it's spoiler-proof. Thanks. I'm devising an experiment to compare the Condorcet method with the IRV method of counting rank choice ballots and would like, if possible, to introduce subjects to the spoiler effect to see under what conditions they notice it occurs. do you want me to tell you how it occurred in Burlington in 2009? -- r b-j r...@audioimagination.com Imagination is more important than knowledge. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
Thanks Robert, My question was strictly about Condorcet and I know already how to generate IRV and spoiler cases, as I said. Are you claiming that Condorcet methods are never subjected to a case of a nonwinning candidate changing who would otherwise win? This seems logical, given the method and what you say below. However,... Do any others on this list agree though or if not, please provide an example? Thanks. Kathy On Wed, Jan 20, 2010 at 7:34 PM, robert bristow-johnson r...@audioimagination.com wrote: On Jan 20, 2010, at 7:10 PM, Kathy Dopp wrote: Is the Condorcet method susceptible to the phenomena of a nonwinning candidate whose presence in the election changes who would otherwise win the election, all else being equal? i changed the sentence form into a question. i hope that was okay, Kathy. don't wanna misquote anyone. i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? in the ranked-order ballot, no matter what their absolute ranks are, if A is ranked above B (or A is ranked while B is not), that counts as a vote for A. likewise for B ranked above A. doesn't matter if they were ranked 4th and 5th. just like the IRV final round between A and B, Condorcet will total how many votes with AB and compare that to votes where BA. whether C is in the race or not, for each individual ballot, if AB with C on the ballot, A would continue to be ranked above B (whether C is higher than either, in between, or below either). with the meaning of every ballot, regarding A and B, unchanged (whether C is there or not), the vote counts for AB and BA do not change. so every Condorcet tally not involving candidate C will remain unchanged, the tallies involving C are not there if C is removed. if A (or whoever is not C) was the Condorcet winner before C was removed, then the AX tally exceeds XA for any X. then A would continue to be ranked over all of the other remaining candidates with the same tallies as before even with C removed, because every tally not involving C would remain unchanged. i would say that (with the CW existing), it's spoiler-proof. Thanks. I'm devising an experiment to compare the Condorcet method with the IRV method of counting rank choice ballots and would like, if possible, to introduce subjects to the spoiler effect to see under what conditions they notice it occurs. do you want me to tell you how it occurred in Burlington in 2009? -- r b-j ...@audioimagination.com Imagination is more important than knowledge. -- Kathy Dopp Town of Colonie, NY 12304 phone 518-952-4030 cell 518-505-0220 http://utahcountvotes.org http://electionmathematics.org http://kathydopp.com/serendipity/ Realities Mar Instant Runoff Voting http://electionmathematics.org/ucvAnalysis/US/RCV-IRV/InstantRunoffVotingFlaws.pdf Voters Have Reason to Worry http://utahcountvotes.org/UT/UtahCountVotes-ThadHall-Response.pdf Checking election outcome accuracy --- Post-election audit sampling http://electionmathematics.org/em-audits/US/PEAuditSamplingMethods.pdf Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 20, 2010, at 7:54 PM, Kathy Dopp wrote: Thanks Robert, My question was strictly about Condorcet and I know already how to generate IRV and spoiler cases, as I said. Are you claiming that Condorcet methods are never subjected to a case of a nonwinning candidate changing who would otherwise win? i said only if there is a Condorcet winner. even though i don't think it would be at all commonplace, much of the discussion between the geeks here sometimes is about exactly what to do for Condorcet cycles. i'm less invested (hell, perhaps if there is a cycle we decide by IRV rules, or pick the candidate with the plurality 1st- choice vote, i really don't care that much) in whatever happens if there is no CW since i don't think it will happen often in real life. -- r b-j r...@audioimagination.com Imagination is more important than knowledge. Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
robert bristow-johnson wrote: i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. MAM/Ranked Pairs is also pretty strategy-resistant and is easier to understand. Schulze has the advantage of producing better results in some cases (closer to Minmax), but if ability to describe to the public is important, then Ranked Pairs wins there. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? (...) i would say that (with the CW existing), it's spoiler-proof. Yes. If there's a CW and a candidate is added, and that candidate doesn't create a cycle, then the winner doesn't change. All the tricky stuff happens when there is a cycle, or the candidate makes one. The advanced methods can claim further resistance: Schulze and Ranked Pairs both make their winner decision independent of candidates not in the Smith set. River is independent of Pareto-dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say YX, and there's at least one such voter). I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work). Election-Methods mailing list - see http://electorama.com/em for list info
Re: [EM] I need an example of Condorcet method being subjected to the spoiler effect if any
On Jan 21, 2010, at 2:29 AM, Kristofer Munsterhjelm wrote: robert bristow-johnson wrote: i think that the answer is no, if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these strategy-resistant methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free. MAM/Ranked Pairs is also pretty strategy-resistant and is easier to understand. Schulze has the advantage of producing better results in some cases (closer to Minmax), but if ability to describe to the public is important, then Ranked Pairs wins there. Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words? (...) i would say that (with the CW existing), it's spoiler-proof. Yes. If there's a CW and a candidate is added, and that candidate doesn't create a cycle, then the winner doesn't change. and if that candidate that is added doesn't *win*. a spoiler is *not* a winner that when removed from the election and all ballots does not change who the winner is. a spoiler must be a loser to the election, whose presence changes who the winner is. i remember reading someone's poor attack on IRV (in local Burlington blogs) that claimed that Bob Kiss (who won Burlington's IRV election) was a spoiler. they were misusing or misunderstanding the concept of a 3rd-party candidate. (maybe somewhere else, a 3rd-party candidate can only hope to be a spoiler, but in Burlington a 3rd-party candidate can expect to win office once in a while. that's a little different.) so, we have a CW... add a candidate, if that candidate does not become the winner, nor cause a cycle, then the Condorcet Winner we had before continues to be the CW with the added candidate. (boy, i guess we're rephrasing the same thing multiple times!) All the tricky stuff happens when there is a cycle, or the candidate makes one. yup. The advanced methods can claim further resistance: Schulze and Ranked Pairs both make their winner decision independent of candidates not in the Smith set. this, i understand... River is independent of Pareto-dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say YX, and there's at least one such voter). i wouldn't mind if someone explains this. i don't know what Pareto- dominated is about. can someone expound? I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work). yes, that's the whole point. this is why i am not yet afraid of someone strategically voting to push a Condorcet election into a cycle. it would be an unsafe way to accomplish a political goal. how could anyone predict what would happen? -- r b-j r...@audioimagination.com Imagination is more important than knowledge. Election-Methods mailing list - see http://electorama.com/em for list info
