Recognition: 1 theorem link
· Lean TheoremThe End Justifies the Mean: A Linear Ranking Rule for Proportional Sequential Decisions
Pith reviewed 2026-05-14 19:52 UTC · model grok-4.3
The pith
The angular mean of voter vectors satisfies long-run individual proportionality for repeated linear rankings.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The main result is that the angular mean, obtained by normalizing the sum of the unit vectors in the directions of each voter type's preferred scoring vector, satisfies long-run individual proportionality: for each voter type i, the long-run fraction of rankings they agree with is at least their population fraction alpha_i. This is achieved because the angular mean balances the directional contributions on the unit sphere rather than allowing vector lengths to dominate.
What carries the argument
The angular mean of the preferred scoring vectors, which normalizes the sum of their unit directions to produce the collective scoring vector theta star.
If this is right
- The arithmetic mean rule is majoritarian and fails proportionality when preferences diverge.
- No fixed linear scoring vector can achieve exact per-batch IP for all voter types.
- The difference between per-batch agreement and long-run agreement decreases rapidly with increasing batch size.
- Performance of all rules is similar under homogeneous preferences, but angular mean improves outcomes substantially under high disagreement.
Where Pith is reading between the lines
- Normalizing vectors before averaging may generalize to other repeated decision settings where direction matters more than magnitude.
- The approach could extend to cases with evolving voter preferences by periodically recomputing the angular mean.
- Testing on larger-scale participatory systems might reveal whether the long-run guarantee translates to perceived fairness.
Load-bearing premise
Long-run average proportionality suffices even if individual batches show large deviations from ideal shares, assuming voter preferences stay constant over batches.
What would settle it
Simulate repeated batches drawn from the item space using the angular mean rule and measure whether the empirical long-run agreement rate for each voter type falls below their population fraction alpha_i.
read the original abstract
AI alignment and participatory design motivate a new democratic design problem: how to collectively choose a decision rule to use repeatedly. We study this problem for linear ranking rules, which repeatedly rank items $x_j$ within batches $X=(x_1,\dots,x_m)\in(\mathbb{R}^d)^m$, where each item's ranking is dictated by its score $\langle \theta^*,x_j\rangle$ according to a fixed scoring vector $\theta^*$. Given voters' preferred scoring vectors $\theta^{(1)},\dots,\theta^{(n)}$ and their population fractions $\alpha^{(1)},\dots,\alpha^{(n)}$, we ask how to choose a collective vector $\theta^*$ satisfying individual proportionality (IP): every voter type $i$ should agree with the resulting rankings to an $\alpha^{(i)}$-proportional degree, either on average over time (long-run IP) or even within each batch (per-batch IP). The default rule, the arithmetic mean of the $\theta^{(i)}$, has been shown to be severely majoritarian; more generally, it is not clear that any fixed linear rule can balance many voters' disparate opinions. Our main result is that, surprisingly, there is a simple rule that does satisfy long-run IP: the angular mean, the spherical analog of the arithmetic mean. We then show that exact per-batch IP is impossible for fixed linear rules, but that the gap between per-batch and long-run IP shrinks quickly with batch size. Experiments on three real-world preference datasets show that all rules perform similarly when voters' preferences are homogeneous, while the angular mean substantially improves proportionality in high-disagreement regimes.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies aggregation of voter preferences θ^(i) with weights α^(i) into a fixed linear scoring vector θ* for repeated ranking of item batches X. It claims that the angular mean θ* = normalize(∑ α^i θ^i) satisfies long-run individual proportionality (IP), meaning each voter type i agrees with the induced rankings (measured by a ranking metric such as fraction of agreeing pairs) to an expected degree exactly proportional to α^i over random batches. It proves that exact per-batch IP is impossible for any fixed linear rule and shows that the per-batch/long-run gap shrinks with batch size m. Experiments on three real-world datasets indicate that the angular mean improves proportionality relative to the arithmetic mean in high-disagreement regimes while performing similarly when preferences are homogeneous.
Significance. If the long-run IP claim holds, the angular mean supplies a simple, parameter-free aggregation rule grounded in spherical geometry that mitigates majoritarianism for sequential linear ranking decisions, with direct relevance to AI alignment and participatory design. The impossibility result for per-batch IP and the quantitative shrinkage with batch size clarify fundamental limits of fixed linear rules. The experimental validation on real preference data strengthens the practical case.
major comments (2)
- [§3 (main theorem)] §3 (main theorem on long-run IP): the claim that θ* = normalize(∑ α^i θ^i) yields exact α^i-proportional expected agreement is not obviously guaranteed. Ranking agreement (e.g., fraction of pairs where sign(⟨θ*, x_a - x_b⟩) matches sign(⟨θ^i, x_a - x_b⟩)) is a nonlinear function of the angle between θ* and θ^i. The vector-sum construction produces linear averaging of directions, but the paper must explicitly verify that the expectation of this nonlinear metric remains proportional to α^i for general item distributions; no such verification or counter-example check is indicated in the provided derivation outline.
- [§4] §4 (per-batch impossibility and gap analysis): while the impossibility of exact per-batch IP for fixed linear rules is correctly established, the rate at which the gap to long-run IP shrinks with batch size m requires an explicit quantitative bound (e.g., via concentration or Lipschitz arguments on the agreement metric). The current statement that the gap “shrinks quickly” is too qualitative to support the practical claim that long-run IP is a sufficient substitute for moderate m.
minor comments (2)
- [Throughout] Notation for voter vectors alternates between θ^{(i)} and θ^i; standardize throughout.
- [Experiments section] The three real-world datasets are referenced only by name; add a brief description of dimensionality d, number of items per batch, and how voter vectors θ^i were estimated.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment below and will revise the paper accordingly.
read point-by-point responses
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Referee: [§3 (main theorem)] §3 (main theorem on long-run IP): the claim that θ* = normalize(∑ α^i θ^i) yields exact α^i-proportional expected agreement is not obviously guaranteed. Ranking agreement (e.g., fraction of pairs where sign(⟨θ*, x_a - x_b⟩) matches sign(⟨θ^i, x_a - x_b⟩)) is a nonlinear function of the angle between θ* and θ^i. The vector-sum construction produces linear averaging of directions, but the paper must explicitly verify that the expectation of this nonlinear metric remains proportional to α^i for general item distributions; no such verification or counter-example check is indicated in the provided derivation outline.
Authors: We agree that the current presentation of the main theorem does not make the verification of the nonlinear expectation fully explicit. The proof sketch in §3 relies on the reduction of expected agreement to a function of the angle under isotropic item distributions, together with the variational property of the angular mean, but this step is not expanded. In the revision we will insert a dedicated lemma deriving the closed-form expected agreement (1 - φ_i/π) and confirming that the resulting values are proportional to α^i as required for long-run IP. revision: yes
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Referee: [§4] §4 (per-batch impossibility and gap analysis): while the impossibility of exact per-batch IP for fixed linear rules is correctly established, the rate at which the gap to long-run IP shrinks with batch size m requires an explicit quantitative bound (e.g., via concentration or Lipschitz arguments on the agreement metric). The current statement that the gap “shrinks quickly” is too qualitative to support the practical claim that long-run IP is a sufficient substitute for moderate m.
Authors: We concur that an explicit rate is needed. We will add to §4 a formal theorem stating that the gap between per-batch and long-run agreement is O(1/sqrt(m)) with high probability. The proof uses the Lipschitz continuity of the pairwise agreement metric (constant independent of m) together with McDiarmid’s inequality applied to the m independent items in the batch. revision: yes
Circularity Check
No significant circularity in angular mean derivation
full rationale
The angular mean is introduced as an independent definition (normalized weighted sum of voter vectors) and the long-run IP property is claimed as a derived result from spherical geometry rather than by construction or tautology. No quoted steps reduce the claimed proportionality to a fitted input, self-citation chain, or renamed known result. The derivation is presented as self-contained against the stated assumptions on fixed preferences and batch sampling; any concerns about nonlinearity of agreement metrics pertain to correctness, not circularity.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Voter preferences are fixed vectors that remain constant across batches
- domain assumption Long-run average agreement is a sufficient fairness criterion
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/AlexanderDuality.leanalexander_duality_circle_linking unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
Our main result is that, surprisingly, there is a simple rule that does satisfy long-run IP: the angular mean, the spherical analog of the arithmetic mean.
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
On the convergence of gradient descent for finding the Riemannian center of mass
Bijan Afsari, Roberto Tron, and Ren \'e Vidal. On the convergence of gradient descent for finding the Riemannian center of mass. SIAM Journal on Control and Optimization, 51 0 (3): 0 2230--2260, 2013
work page 2013
-
[2]
Edmond Awad, Sohan Dsouza, Richard Kim, Jonathan Schulz, Joseph Henrich, Azim Shariff, Jean-Fran c ois Bonnefon, and Iyad Rahwan. The moral machine experiment. Nature, 563 0 (7729): 0 59--64, 2018
work page 2018
-
[3]
On the stability of moral preferences: A problem with computational elicitation methods
Kyle Boerstler, Vijay Keswani, Lok Chan, Jana Schaich Borg, Vincent Conitzer, Hoda Heidari, and Walter Sinnott - Armstrong. On the stability of moral preferences: A problem with computational elicitation methods. In Proceedings of the 2024 AAAI/ACM Conference on AI, Ethics, and Society (AIES), pages 156--167, 2024
work page 2024
-
[4]
Optimal budget aggregation with single-peaked preferences
Felix Brandt, Matthias Greger, Erel Segal - Halevi, and Warut Suksompong. Optimal budget aggregation with single-peaked preferences. In Proceedings of the 25th ACM Conference on Economics and Computation, (EC) , page 49, 2024
work page 2024
-
[5]
Justified representation for perpetual voting
Laurent Bulteau, Noam Hazon, Rutvik Page, Ariel Rosenfeld, and Nimrod Talmon. Justified representation for perpetual voting. IEEE Access , 9: 0 96598--96612, 2021
work page 2021
-
[6]
Samuel R. Buss and Jay P. Fillmore. Spherical averages and applications to spherical splines and interpolation. ACM Transactions on Graphics, 20 0 (2): 0 95--126, 2001
work page 2001
-
[7]
Truthful aggregation of budget proposals with proportionality guarantees
Ioannis Caragiannis, George Christodoulou, and Nicos Protopapas. Truthful aggregation of budget proposals with proportionality guarantees. Artificial Intelligence, 335: 0 104178, 2024
work page 2024
-
[8]
Fr \'e d \'e ric Cazals, Bernard Delmas, and Timothee O'Donnell. Fr \'e chet mean and p -mean on the unit circle: decidability, algorithm, and applications to clustering on the flat torus. In 19th Symposium on Experimental Algorithms (SEA), 2021
work page 2021
-
[9]
Proportional aggregation of preferences for sequential decision making
Nikhil Chandak, Shashwat Goel, and Dominik Peters. Proportional aggregation of preferences for sequential decision making. In Proceedings of the 38th AAAI Conference on Artificial Intelligence (AAAI), pages 9573--9581, 2024
work page 2024
-
[10]
Necessary and sufficient condition for the existence of a Fr \'e chet mean on the circle
Benjamin Charlier. Necessary and sufficient condition for the existence of a Fr \'e chet mean on the circle. ESAIM: Probability and Statistics, 17: 0 635--649, 2013
work page 2013
-
[11]
Paul F. Christiano, Jan Leike, Tom B. Brown, Miljan Martic, Shane Legg, and Dario Amodei. Deep reinforcement learning from human preferences. In Proceedings of the 31st International Conference on Neural Information Processing Systems (NeurIPS), pages 4302--4310, 2017
work page 2017
-
[12]
Vincent Conitzer, Rachel Freedman, Jobst Heitzig, Wesley H. Holliday, Bob M. Jacobs, Nathan Lambert, Milan Moss \' e , Eric Pacuit, Stuart Russell, Hailey Schoelkopf, Emanuel Tewolde, and William S. Zwicker. Position: Social choice should guide AI alignment in dealing with diverse human feedback. In Proceedings of the 41st International Conference on Mach...
work page 2024
-
[13]
Truthful budget aggregation: Beyond moving-phantom mechanisms
Mark de Berg, Rupert Freeman, Ulrike Schmidt - Kraepelin, and Markus Utke. Truthful budget aggregation: Beyond moving-phantom mechanisms. arXiv preprint arXiv:2405.20303, 2024
-
[14]
Settling the score: Portioning with cardinal preferences
Edith Elkind, Matthias Greger, Patrick Lederer, Warut Suksompong, and Nicholas Teh. Settling the score: Portioning with cardinal preferences. Artificial Intelligence, 352: 0 104487, 2026
work page 2026
-
[15]
Michael Feffer, Hoda Heidari, and Zachary C Lipton. Moral machine or tyranny of the majority? In Proceedings of the 37th AAAI Conference on Artificial Intelligence (AAAI), pages 5974--5982, 2023
work page 2023
-
[16]
Adapting a kidney exchange algorithm to align with human values
Rachel Freedman, Jana Schaich Borg, Walter Sinnott-Armstrong, John P Dickerson, and Vincent Conitzer. Adapting a kidney exchange algorithm to align with human values. Artificial Intelligence, 283: 0 103261, 2020
work page 2020
-
[17]
Project-fair and truthful mechanisms for budget aggregation
Rupert Freeman and Ulrike Schmidt - Kraepelin. Project-fair and truthful mechanisms for budget aggregation. In Proceedings of the 38th AAAI Conference on Artificial Intelligence (AAAI) , pages 9704--9712, 2024
work page 2024
-
[18]
Pennock, Dominik Peters, and Jennifer Wortman Vaughan
Rupert Freeman, David M. Pennock, Dominik Peters, and Jennifer Wortman Vaughan. Truthful aggregation of budget proposals. Journal of Economic Theory, 193: 0 105234, 2021
work page 2021
-
[19]
Procaccia, Itai Shapira, Yevgeniy Vorobeychik, and Junlin Wu
Luise Ge, Daniel Halpern, Evi Micha, Ariel D. Procaccia, Itai Shapira, Yevgeniy Vorobeychik, and Junlin Wu. Axioms for AI alignment from human feedback. In Proceedings of the 38th International Conference on Neural Information Processing Systems (NeurIPS), pages 80439--80465, 2024
work page 2024
-
[20]
Enforcing axioms for AI alignment under loss-based rules
Alexandros Hollender and Sonja Kraiczy. Enforcing axioms for AI alignment under loss-based rules. In The 14th International Conference on Learning Representations (ICLR), 2026
work page 2026
-
[21]
Intrinsic means on the circle: uniqueness, locus and asymptotics
Thomas Hotz and Stephan Huckemann. Intrinsic means on the circle: uniqueness, locus and asymptotics. Annals of the Institute of Statistical Mathematics, 67 0 (1): 0 177--193, 2015
work page 2015
-
[22]
Procaccia, and Christos - Alexandros Psomas
Anson Kahng, Min Kyung Lee, Ritesh Noothigattu, Ariel D. Procaccia, and Christos - Alexandros Psomas. Statistical foundations of virtual democracy. In Proceedings of the 36th International Conference on Machine Learning, (ICML), pages 3173--3182, 2019
work page 2019
-
[23]
On the pros and cons of active learning for moral preference elicitation
Vijay Keswani, Vincent Conitzer, Hoda Heidari, Jana Schaich Borg, and Walter Sinnott - Armstrong. On the pros and cons of active learning for moral preference elicitation. In Proceedings of the 2024 AAAI/ACM Conference on AI, Ethics, and Society (AIES) , pages 711--723, 2024
work page 2024
-
[24]
Nguyen, Vincent Conitzer, Hoda Heidari, Jana Schaich Borg, and Walter Sinnott - Armstrong
Vijay Keswani, Cyrus Cousins, Breanna K. Nguyen, Vincent Conitzer, Hoda Heidari, Jana Schaich Borg, and Walter Sinnott - Armstrong. Moral change or noise? on problems of aligning AI with temporally unstable human feedback. In Proceedings of the 40th Conference on Artificial Intelligence, (AAAI), 2026
work page 2026
-
[25]
Richard Kim, Max Kleiman - Weiner, Andr \' e s Abeliuk, Edmond Awad, Sohan Dsouza, Joshua B. Tenenbaum, and Iyad Rahwan. A computational model of commonsense moral decision making. In Proceedings of the 2018 AAAI/ACM Conference on AI, Ethics, and Society (AIES) , pages 197--203, 2018
work page 2018
-
[26]
Optimal bounds for dissatisfaction in perpetual voting
Alexander Kozachinskiy, Alexander Shen, and Tomasz Steifer. Optimal bounds for dissatisfaction in perpetual voting. In Proceedings of the 39th AAAI Conference on Artificial Intelligence (AAAI) , pages 13977--13984, 2025
work page 2025
-
[27]
Perpetual voting: Fairness in long-term decision making
Martin Lackner. Perpetual voting: Fairness in long-term decision making. In Proceedings of the 34th AAAI Conference on Artificial Intelligence (AAAI), pages 2103--2110, 2020
work page 2020
-
[28]
Proportional decisions in perpetual voting
Martin Lackner and Jan Maly. Proportional decisions in perpetual voting. In Proceedings of the 37th AAAI Conference on Artificial Intelligence (AAAI) , pages 5722--5729, 2023
work page 2023
-
[29]
Proportional representation in rank aggregation
Patrick Lederer. Proportional representation in rank aggregation. arXiv preprint arXiv:2508.16177, 2025
-
[30]
The squared kemeny rule for averaging rankings
Patrick Lederer, Dominik Peters, and Tomasz W a s. The squared kemeny rule for averaging rankings. arXiv preprint arXiv:2404.08474, 2024
-
[31]
Min Kyung Lee, Daniel Kusbit, Anson Kahng, Ji Tae Kim, Xinran Yuan, Allissa Chan, Daniel See, Ritesh Noothigattu, Siheon Lee, Alexandros Psomas, and Ariel D. Procaccia. WeBuildAI : Participatory framework for algorithmic governance. Proceedings of the ACM on human-computer interaction, 3 0 (CSCW): 0 1--35, 2019
work page 2019
-
[32]
Jackpot! alignment as a maximal lottery
Roberto - Rafael Maura - Rivero, Marc Lanctot, Francesco Visin, and Kate Larson. Jackpot! alignment as a maximal lottery. arXiv preprint arXiv:2501.19266, 2025
-
[33]
Toponogov’s theorem and applications
Wolfgang Meyer. Toponogov’s theorem and applications. Lecture Notes, Trieste, 1989
work page 1989
-
[34]
Foundations of machine learning
Mehryar Mohri, Afshin Rostamizadeh, and Ameet Talwalkar. Foundations of machine learning. MIT press, 2018
work page 2018
-
[35]
Learning individual and collective priorities over moral dilemmas with the life jacket dataset
Farhad Mohsin, Inwon Kang, Pin-Yu Chen, Francesca Rossi, and Lirong Xia. Learning individual and collective priorities over moral dilemmas with the life jacket dataset. In 13th Multidisciplinary Workshop on Advances in Preference Handling, 2022
work page 2022
-
[36]
A voting-based system for ethical decision making
Ritesh Noothigattu, Snehalkumar Gaikwad, Edmond Awad, Sohan Dsouza, Iyad Rahwan, Pradeep Ravikumar, and Ariel Procaccia. A voting-based system for ethical decision making. In Proceedings of the 32nd AAAI Conference on Artificial Intelligence (AAAI), 2018
work page 2018
-
[37]
Long Ouyang, Jeffrey Wu, Xu Jiang, Diogo Almeida, Carroll L. Wainwright, Pamela Mishkin, Chong Zhang, Sandhini Agarwal, Katarina Slama, Alex Ray, John Schulman, Jacob Hilton, Fraser Kelton, Luke Miller, Maddie Simens, Amanda Askell, Peter Welinder, Paul F. Christiano, Jan Leike, and Ryan Lowe. Training language models to follow instructions with human fee...
work page 2022
-
[38]
Strengthening proportionality in temporal voting
Bradley Phillips, Edith Elkind, Nicholas Teh, and Tomasz Was. Strengthening proportionality in temporal voting. arXiv preprint arXiv:2505.25513, 2025
-
[39]
Procaccia, Benjamin Schiffer, and Shirley Zhang
Ariel D. Procaccia, Benjamin Schiffer, and Shirley Zhang. Clone-robust AI alignment. In Proceedings of the 42nd International Conference on Machine Learning (ICML), 2025
work page 2025
-
[40]
Manning, Stefano Ermon, and Chelsea Finn
Rafael Rafailov, Archit Sharma, Eric Mitchell, Christopher D. Manning, Stefano Ermon, and Chelsea Finn. Direct preference optimization: Your language model is secretly a reward model. In Proceedings of the 36th Conference on Neural Information Processing Systems (NeurIPS), pages 53728--53741, 2023
work page 2023
-
[41]
Philippe Rigollet and Jan-Christian H \"u tter. High-dimensional statistics. arXiv preprint arXiv:2310.19244, 2023
-
[42]
Participatory objective design via preference elicitation
Ali Shirali, Jessie Finocchiaro, and Rediet Abebe. Participatory objective design via preference elicitation. In Proceedings of the 2024 ACM Conference on Fairness, Accountability, and Transparency (FAccT), pages 1637--1662, 2024
work page 2024
- [43]
-
[44]
Distributional preference learning: Understanding and accounting for hidden context in RLHF
Anand Siththaranjan, Cassidy Laidlaw, and Dylan Hadfield - Menell. Distributional preference learning: Understanding and accounting for hidden context in RLHF . In The 12th International Conference on Learning Representations, (ICLR), 2024
work page 2024
-
[45]
Taylor Sorensen, Jared Moore, Jillian Fisher, Mitchell L. Gordon, Niloofar Mireshghallah, Christopher Michael Rytting, Andre Ye, Liwei Jiang, Ximing Lu, Nouha Dziri, Tim Althoff, and Yejin Choi. Position: A roadmap to pluralistic alignment. In Proceedings of the 41st International Conference on Machine Learning, (ICML), volume 235, pages 46280--46302, 2024
work page 2024
-
[46]
Riemannian spaces having their curvature bounded below by a positive number
Victor Andreevich Toponogov. Riemannian spaces having their curvature bounded below by a positive number. Twenty-Two Papers on Algebra, Number Theory and Differential Geometry, pages 291--336, 1964
work page 1964
-
[47]
David E. Tyler. Statistical analysis for the angular central G aussian distribution on the sphere. Biometrika, 74 0 (3): 0 579--589, 1987
work page 1987
-
[48]
High-dimensional statistics: A non-asymptotic viewpoint
Martin J Wainwright. High-dimensional statistics: A non-asymptotic viewpoint. Cambridge University Press, 2019
work page 2019
-
[49]
Haoxiang Wang, Yong Lin, Wei Xiong, Rui Yang, Shizhe Diao, Shuang Qiu, Han Zhao, and Tong Zhang. Arithmetic control of llms for diverse user preferences: Directional preference alignment with multi-objective rewards. In Proceedings of the 62nd Annual Meeting of the Association for Computational (ACL), pages 8642--8655, 2024 a
work page 2024
-
[50]
Interpretable preferences via multi-objective reward modeling and mixture-of-experts
Haoxiang Wang, Wei Xiong, Tengyang Xie, Han Zhao, and Tong Zhang. Interpretable preferences via multi-objective reward modeling and mixture-of-experts. In Findings of the Association for Computational Linguistics. Association for Computational Linguistics, 2024 b
work page 2024
discussion (0)
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