Reliable Conformal Prediction for Ordinal Classification Using the Ranked Probability Score
Pith reviewed 2026-06-26 00:41 UTC · model grok-4.3
The pith
The ranked probability score as nonconformity measure produces median-centered contiguous prediction sets by construction in conformal prediction for ordinal classification.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
When the ranked probability score serves as the nonconformity measure, conformal prediction for ordinal classification yields median-centered contiguous prediction sets by construction. The procedure remains model-agnostic, applies to assessed or grouped ordered categories, and runs efficiently without greedy interval search, while experiments show competitive trade-offs between set size and ordinal error magnitude.
What carries the argument
The ranked probability score used as a nonconformity measure, which by construction produces contiguous and median-centered prediction sets.
If this is right
- Prediction sets remain contiguous without any additional selection procedure.
- Sets are centered on the median prediction by design.
- The method applies directly to both assessed and grouped ordered outcomes.
- Implementation is more efficient than greedy interval selection methods.
- Sets achieve a balance between width and the magnitude of ordinal miscoverage.
Where Pith is reading between the lines
- The construction could simplify deployment of ordinal conformal methods in practice by removing the need for custom contiguity enforcement.
- Similar scoring rules that respect cumulative distributions might be tested for analogous automatic properties in other structured prediction settings.
- High-stakes applications could measure whether the median-centering reduces costly ordinal errors more than width-minimizing alternatives.
Load-bearing premise
The ranked probability score functions as an effective nonconformity measure that automatically enforces contiguity and median-centering without further assumptions or post-processing.
What would settle it
Finding a dataset and model where RPS-based conformal sets are neither contiguous nor median-centered would falsify the construction claim.
Figures
read the original abstract
Ordinal classification (OC) arises in high-stakes domains such as medicine and finance, where uncertainty quantification must account for the severity of ordinal errors. Conformal prediction (CP) provides distribution-free prediction sets with marginal coverage guarantees; however, its practical effectiveness depends critically on the choice of nonconformity function. We introduce a CP method for ordinal classification based on the ranked probability score (RPS), a proper scoring rule defined over cumulative predictive distributions. Although it reflects ordinal risk quite naturally, it has largely been neglected in conformal ordinal prediction (COP). When used as a measure of nonconformity, RPS yields median-centered contiguous prediction sets by construction. The method is model-agnostic, supports both assessed and grouped ordered categorical outcomes, and permits efficient implementation compared to greedy interval selection procedures. Across multiple ordinal image and tabular datasets, RPS-based CP produces contiguous prediction sets and strikes a favorable balance between prediction set width and the magnitude of ordinal miscoverage relative to existing CP methods.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes using the ranked probability score (RPS) as a nonconformity measure within conformal prediction for ordinal classification. It claims that this produces median-centered contiguous prediction sets by construction under standard exchangeability, without post-processing or extra assumptions. The method is model-agnostic, supports assessed and grouped outcomes, and is claimed to be computationally efficient. Empirical evaluations on ordinal image and tabular datasets are said to show a favorable balance between prediction-set width and ordinal miscoverage relative to prior conformal methods.
Significance. If the construction holds, the result supplies a parameter-free, proper-scoring-rule-based nonconformity measure that automatically enforces contiguity and median centering while retaining the usual marginal coverage guarantee. This is a practical advantage for ordinal problems in medicine and finance. Credit is due for the explicit verification that RPS sublevel sets are intervals containing the median (shown via contradiction for K=3 and K=4) and for the absence of invented entities or circular parameters.
minor comments (2)
- The abstract states that RPS 'yields median-centered contiguous prediction sets by construction,' yet the provided verification is limited to K=3 and K=4; a compact general argument (or reference to the known monotonicity of RPS away from the median) would make the claim self-contained for arbitrary K.
- The efficiency claim relative to 'greedy interval selection procedures' is asserted but not quantified; adding a brief complexity comparison or runtime table would strengthen the practical contribution without altering the central result.
Simulated Author's Rebuttal
We thank the referee for the positive summary, significance assessment, and recommendation of minor revision. The feedback highlights the practical advantages of the RPS nonconformity measure, which aligns with our claims.
Circularity Check
No significant circularity
full rationale
The paper's central result—that RPS as nonconformity score produces median-centered contiguous sets by construction—follows from the explicit mathematical property of the ranked probability score (minimized at the median of any fixed CDF F, with sublevel sets forming intervals), which is verified directly for small K without reference to fitted parameters from the target data or self-citations. Coverage remains the standard marginal guarantee under exchangeability; no step reduces a claimed prediction to an input by definition or via load-bearing self-citation. The empirical comparisons are separate and do not affect the derivation.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Data points are exchangeable, enabling marginal coverage guarantees in conformal prediction.
- standard math Ranked probability score is a proper scoring rule that penalizes ordinal distance appropriately.
Reference graph
Works this paper leans on
-
[1]
Ordinal losses for classification of cervical cancer risk , journal =
Tom. Ordinal losses for classification of cervical cancer risk , journal =. 2021 , doi =
2021
-
[2]
Pattern Recognit
Wenzhi Cao and Vahid Mirjalili and Sebastian Raschka , title =. Pattern Recognit. Lett. , volume =. 2020 , doi =
2020
-
[3]
Ordinal Regression Methods: Survey and Experimental Study , journal =
Pedro Antonio Guti. Ordinal Regression Methods: Survey and Experimental Study , journal =. 2016 , doi =
2016
-
[4]
AAAI-25, Sponsored by the Association for the Advancement of Artificial Intelligence, February 25 - March 4, 2025, Philadelphia, PA,
Inbar Nachmani and Bar Genossar and Coral Scharf and Roee Shraga and Avigdor Gal , title =. AAAI-25, Sponsored by the Association for the Advancement of Artificial Intelligence, February 25 - March 4, 2025, Philadelphia, PA,. 2025 , doi =
2025
-
[5]
Pattern Anal
Xintong Shi and Wenzhi Cao and Sebastian Raschka , title =. Pattern Anal. Appl. , volume =. 2023 , doi =
2023
-
[6]
Angelopoulos and Stephen Bates , title =
Anastasios N. Angelopoulos and Stephen Bates , title =. CoRR , volume =. 2021 , eprinttype =. 2107.07511 , timestamp =
Pith/arXiv arXiv 2021
-
[7]
Journal of the Royal Statistical Society: Series B (Methodological) , volume=
Regression models for ordinal data , author=. Journal of the Royal Statistical Society: Series B (Methodological) , volume=. 1980 , publisher=
1980
-
[8]
Tayyab Bin Tariq and Zobia Suhail and Zubair Nawaz , title =. Multim. Tools Appl. , volume =. 2025 , doi =
2025
-
[9]
Journal of Hepatology , volume=
An ordinal model to predict the risk of symptomatic liver failure in patients with cirrhosis undergoing hepatectomy , author=. Journal of Hepatology , volume=. 2019 , publisher=
2019
-
[10]
Machine learning , volume=
Aleatoric and epistemic uncertainty in machine learning: An introduction to concepts and methods , author=. Machine learning , volume=. 2021 , publisher=
2021
-
[11]
Uncertainty quantification in ordinal classification:
Stefan Haas and Eyke H. Uncertainty quantification in ordinal classification:. Int. J. Approx. Reason. , volume =. 2025 , doi =
2025
-
[12]
Stefan Haas and Eyke H. Aleatoric and Epistemic Uncertainty Measures for Ordinal Classification through Binary Reduction , journal =. 2025 , doi =. 2507.00733 , timestamp =
arXiv 2025
-
[13]
, author=
Weighted kappa: Nominal scale agreement provision for scaled disagreement or partial credit. , author=. Psychological bulletin , volume=. 1968 , publisher=
1968
-
[14]
Advances in Artificial Intelligence, 22nd Canadian Conference on Artificial Intelligence, Canadian
Lisa Gaudette and Nathalie Japkowicz , title =. Advances in Artificial Intelligence, 22nd Canadian Conference on Artificial Intelligence, Canadian. 2009 , doi =
2009
-
[15]
Rectifying Bias in Ordinal Observational Data Using Unimodal Label Smoothing , booktitle =
Stefan Haas and Eyke H. Rectifying Bias in Ordinal Observational Data Using Unimodal Label Smoothing , booktitle =. 2023 , doi =
2023
-
[16]
Pinto da Costa and Hugo Alonso and Jaime S
Joaquim F. Pinto da Costa and Hugo Alonso and Jaime S. Cardoso , title =. Neural Networks , volume =. 2008 , doi =
2008
-
[17]
Unimodal regularisation based on beta distribution for deep ordinal regression , journal =
V. Unimodal regularisation based on beta distribution for deep ordinal regression , journal =. 2022 , doi =
2022
-
[18]
Pal , title =
Christopher Beckham and Christopher J. Pal , title =. Proceedings of the 34th International Conference on Machine Learning,. 2017 , timestamp =
2017
-
[19]
Kaveri , title =
Prasenjit Dey and Srujana Merugu and Sivaramakrishnan R. Kaveri , title =. Advances in Neural Information Processing Systems 36: Annual Conference on Neural Information Processing Systems 2023, NeurIPS 2023, New Orleans, LA, USA, December 10 - 16, 2023 , year =
2023
-
[20]
Class distance weighted cross entropy loss for classification of disease severity , journal =
Gorkem Polat and. Class distance weighted cross entropy loss for classification of disease severity , journal =. 2025 , doi =
2025
-
[21]
Squared Earth Mover's Distance-based Loss for Training Deep Neural Networks , journal =
Le Hou and Chen. Squared Earth Mover's Distance-based Loss for Training Deep Neural Networks , journal =. 2016 , eprinttype =. 1611.05916 , timestamp =
Pith/arXiv arXiv 2016
-
[22]
Generalised triangular distributions for ordinal deep learning: Novel proposal and optimisation , journal =
V. Generalised triangular distributions for ordinal deep learning: Novel proposal and optimisation , journal =. 2023 , doi =
2023
-
[23]
2019 , timestamp =
Raul Diaz and Amit Marathe , title =. 2019 , timestamp =
2019
-
[24]
Weighted kappa loss function for multi-class classification of ordinal data in deep learning , journal =
Jordi de La Torre and Domenec Puig and A. Weighted kappa loss function for multi-class classification of ordinal data in deep learning , journal =. 2018 , doi =
2018
-
[25]
Rainer Hirk and Kurt Hornik and Laura Vana , title =. Stat. Methods Appl. , volume =. 2019 , doi =
2019
-
[26]
Dynamically weighted evolutionary ordinal neural network for solving an imbalanced liver transplantation problem , journal =
Manuel Dorado. Dynamically weighted evolutionary ordinal neural network for solving an imbalanced liver transplantation problem , journal =. 2017 , doi =
2017
-
[27]
2005 , publisher=
Algorithmic learning in a random world , author=. 2005 , publisher=
2005
-
[28]
Proceedings of the Sixteenth International Conference on Machine Learning
Volodya Vovk and Alexander Gammerman and Craig Saunders , title =. Proceedings of the Sixteenth International Conference on Machine Learning. 1999 , timestamp =
1999
-
[29]
Glenn Shafer and Vladimir Vovk , title =. J. Mach. Learn. Res. , volume =. 2008 , doi =
2008
-
[30]
Yaniv Romano and Evan Patterson and Emmanuel J. Cand. Conformalized Quantile Regression , booktitle =. 2019 , timestamp =
2019
-
[31]
2008 , publisher=
Inductive conformal prediction: Theory and application to neural networks , author=. 2008 , publisher=
2008
-
[32]
Angelopoulos and Stuart R
Charles Lu and Anastasios N. Angelopoulos and Stuart R. Pomerantz , title =. Medical Image Computing and Computer Assisted Intervention -. 2022 , doi =
2022
-
[33]
Uncertainty in Artificial Intelligence,
Yunpeng Xu and Wenge Guo and Zhi Wei , title =. Uncertainty in Artificial Intelligence,. 2023 , timestamp =
2023
-
[34]
Fortieth
Zijian Zhang and Xinyu Chen and Yuanjie Shi and Liyuan Lillian Ma and Zifan Xu and Yan Yan , title =. Fortieth. 2026 , doi =
2026
-
[35]
A Simple Log-based Loss Function for Ordinal Text Classification , booktitle =
Fran. A Simple Log-based Loss Function for Ordinal Text Classification , booktitle =. 2022 , timestamp =
2022
-
[36]
Stefan Kramer and Gerhard Widmer and Bernhard Pfahringer and Michael de Groeve , title =. Fundam. Informaticae , volume =. 2001 , timestamp =
2001
-
[37]
Yaniv Romano and Matteo Sesia and Emmanuel J. Cand. Classification with Valid and Adaptive Coverage , booktitle =. 2020 , timestamp =
2020
-
[38]
Journal of the American Statistical Association , volume=
Least ambiguous set-valued classifiers with bounded error levels , author=. Journal of the American Statistical Association , volume=. 2019 , publisher=
2019
-
[39]
Angelopoulos and Stephen Bates and Adam Fisch and Lihua Lei and Tal Schuster , title =
Anastasios N. Angelopoulos and Stephen Bates and Adam Fisch and Lihua Lei and Tal Schuster , title =. CoRR , volume =. 2022 , doi =. 2208.02814 , timestamp =
arXiv 2022
-
[40]
Journal of Applied Meteorology (1962-1982) , volume=
A scoring system for probability forecasts of ranked categories , author=. Journal of Applied Meteorology (1962-1982) , volume=. 1969 , publisher=
1962
-
[41]
Journal of the American statistical Association , volume=
Strictly proper scoring rules, prediction, and estimation , author=. Journal of the American statistical Association , volume=. 2007 , publisher=
2007
-
[42]
Vladimir Vovk , title =. Mach. Learn. , volume =. 2013 , doi =
2013
-
[43]
Jordan and Jitendra Malik , title =
Anastasios Nikolas Angelopoulos and Stephen Bates and Michael I. Jordan and Jitendra Malik , title =. 9th International Conference on Learning Representations,. 2021 , timestamp =
2021
-
[44]
Machine Learning:
Harris Papadopoulos and Kostas Proedrou and Volodya Vovk and Alex Gammerman , title =. Machine Learning:. 2002 , doi =
2002
-
[45]
Monthly weather review , volume=
Verification of forecasts expressed in terms of probability , author=. Monthly weather review , volume=. 1950 , publisher=
1950
-
[46]
Jose and Robert F
Victor Richmond R. Jose and Robert F. Nau and Robert L. Winkler , title =. Manag. Sci. , volume =. 2009 , doi =
2009
-
[47]
Medical Image Computing and Computer Assisted Intervention -
Adrian Galdran , title =. Medical Image Computing and Computer Assisted Intervention -. 2023 , doi =
2023
-
[48]
Monthly Weather Review , volume=
The ranked probability score and the probability score: A comparison , author=. Monthly Weather Review , volume=
-
[49]
1971 , journal =
Some results for discrete unimodality , author =. 1971 , journal =
1971
-
[50]
Mathematics , volume=
Quasi-unimodal distributions for ordinal classification , author=. Mathematics , volume=. 2022 , publisher=
2022
-
[51]
Cardoso and Ricardo P
Jaime S. Cardoso and Ricardo P. M. Cruz and Tom. Unimodal Distributions for Ordinal Regression , journal =. 2025 , doi =
2025
-
[52]
Neurocomputing , volume =
Xiaofeng Liu and Fangfang Fan and Lingsheng Kong and Zhihui Diao and Wanqing Xie and Jun Lu and Jane You , title =. Neurocomputing , volume =. 2020 , doi =
2020
-
[53]
Soft labelling based on triangular distributions for ordinal classification , journal =
V. Soft labelling based on triangular distributions for ordinal classification , journal =. 2023 , doi =
2023
-
[54]
The 13th Symposium on Conformal and Probabilistic Prediction with Applications, 9-11 September 2024, Politecnico di Milano, Milano, Italy , series =
Subhrasish Chakraborty and Chhavi Tyagi and Haiyan Qiao and Wenge Guo , title =. The 13th Symposium on Conformal and Probabilistic Prediction with Applications, 9-11 September 2024, Politecnico di Milano, Milano, Italy , series =. 2024 , timestamp =
2024
-
[55]
Journal of the Royal Statistical Society: Series B (Methodological) , volume=
Regression and ordered categorical variables , author=. Journal of the Royal Statistical Society: Series B (Methodological) , volume=. 1984 , publisher=
1984
-
[56]
Age Estimation Using Soft Labelling Ordinal Classification Approaches , booktitle =
V. Age Estimation Using Soft Labelling Ordinal Classification Approaches , booktitle =. 2024 , doi =
2024
-
[57]
Cordier, Thibault and Blot, Vincent and Lacombe, Louis and Morzadec, Thomas and Capitaine, Arnaud and Brunel, Nicolas , booktitle =
-
[58]
Fan and Daniel Nouri and Benjamin Bossan and
Marian Tietz and Thomas J. Fan and Daniel Nouri and Benjamin Bossan and. skorch: A scikit-learn compatible neural network library that wraps PyTorch , month = jul, year = 2017, url =
2017
-
[59]
and Varoquaux, G
Pedregosa, F. and Varoquaux, G. and Gramfort, A. and Michel, V. and Thirion, B. and Grisel, O. and Blondel, M. and Prettenhofer, P. and Weiss, R. and Dubourg, V. and Vanderplas, J. and Passos, A. and Cournapeau, D. and Brucher, M. and Perrot, M. and Duchesnay, E. , journal=. Scikit-learn: Machine Learning in
-
[60]
Advances in neural information processing systems , volume=
Pytorch: An imperative style, high-performance deep learning library , author=. Advances in neural information processing systems , volume=
-
[61]
dlordinal:
Francisco B. dlordinal:. Neurocomputing , volume =. 2025 , doi =
2025
-
[62]
ranked probability score
On the “ranked probability score” , author=. Journal of Applied Meteorology and Climatology , volume=
-
[63]
Journal of Applied Meteorology , year=
A Note on the Ranked Probability Score , author=. Journal of Applied Meteorology , year=
-
[64]
TOC-UCO: a comprehensive repository of tabular ordinal classification datasets , journal =. 2026 , issn =. doi:https://doi.org/10.1016/j.neucom.2026.133528 , author =
-
[65]
LightGBM:
Guolin Ke and Qi Meng and Thomas Finley and Taifeng Wang and Wei Chen and Weidong Ma and Qiwei Ye and Tie. LightGBM:. Advances in Neural Information Processing Systems 30: Annual Conference on Neural Information Processing Systems 2017, December 4-9, 2017, Long Beach, CA,. 2017 , timestamp =
2017
-
[66]
Luben M. C. Cabezas and Vagner S. Santos and Thiago Ramos and Rafael Izbicki , title =. Conference on Uncertainty in Artificial Intelligence, Rio Othon Palace, Rio de Janeiro, Brazil, 21-25 July 2025 , series =. 2025 , timestamp =
2025
-
[67]
Medical Image Analysis , volume=
BACH: Grand challenge on breast cancer histology images , author=. Medical Image Analysis , volume=. 2019 , publisher=
2019
-
[68]
Nature inspired smart information systems (NiSIS 2005) , pages=
Pap-smear benchmark data for pattern classification , author=. Nature inspired smart information systems (NiSIS 2005) , pages=
2005
-
[69]
2009 IEEE conference on computer vision and pattern recognition , pages=
Imagenet: A large-scale hierarchical image database , author=. 2009 IEEE conference on computer vision and pattern recognition , pages=. 2009 , organization=
2009
-
[70]
Kaiming He and Xiangyu Zhang and Shaoqing Ren and Jian Sun , title =. 2016. 2016 , doi =
2016
-
[71]
Scientific Data , volume=
MedMNIST v2-A large-scale lightweight benchmark for 2D and 3D biomedical image classification , author=. Scientific Data , volume=. 2023 , publisher=
2023
-
[72]
IEEE Transactions on pattern Analysis and machine Intelligence , volume=
Toward automatic simulation of aging effects on face images , author=. IEEE Transactions on pattern Analysis and machine Intelligence , volume=. 2002 , publisher=
2002
-
[73]
Iet Biometrics , volume=
Overview of research on facial ageing using the FG-NET ageing database , author=. Iet Biometrics , volume=. 2016 , publisher=
2016
-
[74]
, year =
Melanoma on a patient's skin. , year =
-
[75]
arXiv preprint arXiv:2505.19033 , year=
Optimal conformal prediction under epistemic uncertainty , author=. arXiv preprint arXiv:2505.19033 , year=
-
[76]
2025 , publisher=
Aleatoric and Epistemic Uncertainty in Conformal Prediction , author=. 2025 , publisher=
2025
-
[77]
Information fusion , volume=
Tabular data: Deep learning is not all you need , author=. Information fusion , volume=. 2022 , publisher=
2022
-
[78]
Advances in Neural Information Processing Systems 31: Annual Conference on Neural Information Processing Systems 2018, NeurIPS 2018, December 3-8, 2018, Montr
Liudmila Ostroumova Prokhorenkova and Gleb Gusev and Aleksandr Vorobev and Anna Veronika Dorogush and Andrey Gulin , title =. Advances in Neural Information Processing Systems 31: Annual Conference on Neural Information Processing Systems 2018, NeurIPS 2018, December 3-8, 2018, Montr. 2018 , timestamp =
2018
-
[79]
Proceedings of the 22nd
Tianqi Chen and Carlos Guestrin , title =. Proceedings of the 22nd. 2016 , doi =
2016
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