BTR-score
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BTW, my sims include "STAR3", which is literally BTR via Score among just the top 3 candidates.
You can see it's extremely similar in batch simulated results to BTR and Condorcet//Plurality or Smith//Plurality.Your simulator is amazing and useful.
I am looking for the best voting methods for single-winner and proportional elections.
I am starting an advocacy organization, Voters Take Charge, to sell those methods.
The ideal method would combine performance with ease of explanation.
The methods need to be good because the people selling RCV have more money than me and the defenders of the status quo have near infinite resources.Performance criteria:
Fairness! As determined by the voting public and the members of this forum.
Resist strategy, both organized strategy and strategy by individual voters.
No spoiler effect / favorite betrayal.
Able to deal with clones and irrelevant alternatives.
Rarely screw up in elections with over 1,000 voters.Below is a list of single-winner systems, from the easiest to the most difficult to explain.
Score - Explain Score voting. Easy, but I am concerned about strategy resistance.
STAR - Explain Score voting and a two-way pairwise runoff. Pretty easy for a hybrid system.
BTR / Score - Explain Score and a series of pairwise runoffs between the bottom 2 candidates. Not too bad.
IRV - Explain counting in rounds with the transfer of “2nd choice votes”. Not easy, but only one process.
Condorcet / Hare - Explain a round robin pairwise tournament and counting in rounds with the transfer of ‘’2nd choice votes”. It helps that some people know about round robin and RCV.
STAR 3 - Explain Score voting with normalization and a three-way pairwise runoff. A lot of work.Two Questions:
Which of the above has the best combination of performance and ease of explanation?
Are there other single-winner system I should consider? -
BTW, my sims include "STAR3", which is literally BTR via Score among just the top 3 candidates.
I found a fairly easy to explain voting method on your sims list, Smith-Plurality. Just need to describe a round robin, pairwise tournament. I ran a few sims, Smith-Plurality seems to hold it's own. It must be the simplest Condorcet tie breaker. I am surprised this is not popular, is there something wrong that I am missing?
Smith-Score would be ok but re-normalization would need to be explained. Not too bad, is there another word for re-normalization? It sound like something out of 1984.
Concerning Strategy Present, filtered and unfiltered; do these include organized and/or individual voter strategies?
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@casimir you indicated that the second-highest score winner in the cycle will be elected in a 4-cycle. This means that lowering the score of a candidate can cause them to win in such a case, which practically speaking is a very rare case.
I’m only speaking in terms of the strict criterion, I also don’t care if a method is super rarely non-monotonic. But I didn’t think that was @Jack-Waugh’s question.
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I think you have the wrong guy. Insofar as I spoke about monotonicity, I was making the opposite argument.
If a court wishes to "ban non-monotonic voting methods", they would first have to declare all partisan primaries illegal.
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@chocopi Sorry, it was @Lime https://www.votingtheory.org/forum/post/3716
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In this new ordering, Paper Jr. takes out Rock early, preventing Rock from taking out Scissors. Now Scissors wins.
This is, of course, an extremely specific scenario--and a good illustration of why focusing on absolute criteria is misleading. No one should care that something like BTR or Stable Voting are non-monotonic one-in-a-gazillion elections.
Thank you. I missed that case. In the list I provided this corresponds to [B]CAD turning to B[A]CD.
Smith-Score would be ok but re-normalization would need to be explained.
There might be a misunderstanding. The normalization of ballots is an assumptions of voter behavior, not part of the method. Smith//plurality misses that paragraph because it uses a ranked ballot instead of rated like Smith//score.
@casimir you indicated that the second-highest score winner in the cycle will be elected in a 4-cycle. This means that lowering the score of a candidate can cause them to win in such a case, which practically speaking is a very rare case.
Take a look at the list I provided. It has some cases where the second highest candidate wins, but no case where lowering the score of a candidate causes them to win instead of someone else. Likewise, raising someones score won't cause them to loose. The case that @chocopi pointed out is one where changing the order of the other candidates causes someone to loose. It's weird, but it's no reason to not give your favorite candidate full support (except for the favorite betrayal case, which comes with being a Condorcet method).
Because I'm from Germany, monotonicity is somewhat relevant, but it's not that all non-monotonic methods are banned.
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@casimir what I mean is that, in the realm of score perturbations that keep a given 4-cycle in tact, the ultimate goal would be to have given your favorite candidate a score such that they receive the second-highest sum of scores, not the first-highest. Does that make sense?
Again, it’s a weird, seemingly irrelevant edge case. But as you mention, it might not be irrelevant in situations where there are strict laws about monotonicity.
For the record, I really like BTR. It’s one of my favorite methods. It’s highly efficient to say the least. And your claims about how well it conforms to monotonicity make me like it even more, since my main concern about it from the beginning has been monotonicity.
I consider it a “cardinal-Condorcet” method, which I rate a 9 out of 10. It can be made even more monotonically robust by extending from “eliminate the bottom 2 Condorcet loser” to “eliminate the bottom N Condorcet loser” for N>2.
I’m not sure if N=K (the number of candidates) succeeds in full monotonicity, but I wager it does.
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I'm not sure I understand the question. In which case would it be beneficial to have your favorite placed second by score?
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@casimir suppose you submit your ballots, and then A,B,C,D are in the top 4-cycle. If your favorite is A, maybe you reasonably gave them your highest score. Now suppose A also has the highest aggregated score among the 4. Then, they will lose to the second-highest scoring candidate X≠A. So perhaps if you had lowered the score of A (without going below your second favorite among the 4–B, say), maybe A would have won instead of X.
Also, as you mention, it’s possible that by being dishonest about preferences below A, one could avoid the top cycle situation and lean on the highest score angle. I don’t have the details fleshed out.
Super niche and a really improbable situation. And maybe even an impossible situation, but I’m not sure it’s actually impossible.
Last note is that finding a single Condorcet loser is also generally more efficient than computing the entire preference matrix. With dynamic programming, taking the bottom N>2 may also be fairly efficient.
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Here are all the permutation of a 4-cycle:
C[A]BD B[A]CD C[A]DB B[A]DC [A]CBD [A]BCD [A]CDB [A]BDC [A]DCB [A]DBC C[B]AD [D]CAB C[B]DA [D]CBA [B]CAD [D]ACB [B]CDA [D]ABC [B]DAC [D]BCA [B]DCA [D]BAC [C]DBA [C]DABOut of these there are six cases where the second highest candidate wins.
C[A]BD B[A]CD C[B]AD C[A]DB B[A]DC C[B]DAFor this to be a problem there should exist an alternative where the first and second placed candidates swap, but the new second place wins. But looking at the options above, there is non where C wins in second place. Also, for the B first cases, swapping B and A still leaves A winning. So, at least in a 4-cycle, this is not an issue.
As for FB, it fails the same way as this example with for example candidates ordered form high to low score as D A B C.
All that said, I'm mostly concerned with practicality. For me the purpose of BTR-score is to be an as-simple-as-possible Condorcet method. Any way to make it compliant with more criteria would also make it more complex. It's good to know what properties it has, but I have no strict requirements. If it is non-monotonic in some rare cases, so be it - as long as it has no overt issues like Copeland does.
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If a court wishes to "ban non-monotonic voting methods", they would first have to declare all partisan primaries illegal.
I'd agree with you. In practice, partisan primaries determine which candidates you can actually vote for (because of the two-party system). But from a purely legal point of view, a partisan primary isn't "part of the election"; it's just a private association making a decision about who to support.
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@jack-waugh said in BTR-score:
it's just a private association making a decision about whom to support.
If it is a private decision, then why does the public have to pay for it (in the US)?
Good question. You can ask the Supreme Court.
https://en.wikipedia.org/wiki/California_Democratic_Party_v._Jones -
@jack-waugh said in BTR-score:
If it is a private decision, then why does the public have to pay for it (in the US)?
The justification for taxpayer funded closed primary elections is the theory that a even a closed primary offers more voter participation than nomination by caucus or party leadership.
Primaries, open, semi-open, and closed, provide free publicity to major political parties and establish a certain legitimacy to the major parties.
I am weird, I think we should offer each and every party the choice of an open, semi-open, closed or no primary elections. This would help third parties. This will also never happen.
One alternative is let parties nominate candidates as they see fit. If their are more than seven candidates, hold a blanket primary to narrow the field to three or four candidates, two candidates if plurality voting will be used.
The leading purveyors of RCV, the Top Four & Final Five folks, want to do this in a manor to screw political parties and help unaffiliated candidates. What they call "nonpartisan"; party nominations are not listed on the ballot but party affiliations of each candidate (from voter registration records) are listed on the ballots. This are "confused partisan" rather than "nonpartisan" elections.
They want to the nominees of political parties to be subject the same signature requirements as unaffiliated candidates. Unaffiliated candidates would have the advantages of not having to qualify for party status and not be responsible to party members.
All this signature gathering would drive up the cost of nomination signatures. Wealthy independents and major parties would get their signatures, more difficult for third party and independents who are not wealthy .
The dream of the Top Four and Final Five leaders is to elect a small squad of "moderate" (wealthy, donner class light) independents that would seize the balance of power in America.
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In summary, does anyone have a serious objection to the idea of all of us promoting this system for all cases where there isn't already a big investment in Score (including Approval) or STAR?
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@jack-waugh I like the system in theory, it’s a pretty conservative cardinal Condorcet method. I’d like to see more examples of how it resolves when there is no Condorcet winner. I also think it can be improved to Bottom N Runoff (BNR) and made more conservative, although BTR has a simpler description.
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@jack-waugh
It might still be too complex for voters without prior education. As someone immersed in these discussions, it is easy to loose sight of how little people know about voting and how many conceptual steps people have to take before understanding the method. I've argued here that it might be more useful to promote a spectrum of compatible methods (approval, score, STAR and BTR-score in this case). -
@casimir, thanks, that's a very interesting write-up.
At the end, you suggest that the equal-vote criterion would be too restrictive as a minimal standard. But all four of those systems pass it, I believe. They are additive and Frohnmayer-balancing.
