Recognition: unknown
Random-Effects Algorithm for Random Objects in Metric Spaces
Pith reviewed 2026-05-08 17:16 UTC · model grok-4.3
The pith
A nonlinear Fréchet-based algorithm delivers consistent random-effects prediction for arbitrary objects in metric spaces.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We propose a nonlinear Fréchet-based algorithm for random-effects modeling of arbitrary random objects defined on a metric space. Using M-estimation theory, we establish conditions under which the proposed metric-space prediction target is consistently estimated under a working random-effects formulation. We then evaluate the empirical performance of the proposed method using both synthetic data and digital health datasets that require practical tools for analyzing random objects in metric spaces, such as multivariate probability distributions and random graphs. We show that, although our method is developed beyond Hilbert spaces, it can outperform existing Hilbert space-based methods.
What carries the argument
Nonlinear Fréchet-based random-effects algorithm, which replaces Euclidean operations with Fréchet means and regressions defined directly in the metric space to produce a consistent prediction target.
If this is right
- Random-effects borrowing of strength becomes available for repeated non-Euclidean observations such as random graphs or probability distributions.
- Personalized prediction targets can be formed for metric-space outcomes with explicit consistency guarantees.
- The same working-model strategy applies to any metric space once the Fréchet operations are well-defined.
- Digital-health analyses that previously required Euclidean approximations can now use the native geometry of the data.
Where Pith is reading between the lines
- The working random-effects formulation may still produce useful shrinkage even when the true data-generating process is not exactly a random-effects model.
- The approach could be tested on longitudinal metric-space data where the metric itself changes over time.
- Because the method works in general metric spaces, it offers a route to unify random-effects modeling across shape analysis, network data, and distributional data.
- Extensions to time-to-event or censored observations in metric spaces would follow the same M-estimation template.
Load-bearing premise
The metric space and random objects must satisfy the technical conditions required for M-estimation to deliver consistent estimation of the prediction target under the working random-effects model.
What would settle it
A simulation in which the algorithm's estimated prediction target exhibits persistent bias or fails to converge to the true target as the number of units and observations per unit increase, despite the metric space satisfying all stated M-estimation regularity conditions.
Figures
read the original abstract
Across many scientific disciplines, multiple observations are collected from the same experimental units, and in modern datasets these observations often arise as non-Euclidean random objects. In such settings, the incorporation of random effects is a critical modeling step for efficient estimation and personalized prediction. Although mixed-effects models are well established for scalar outcomes and, more recently, for functional data in Hilbert spaces, general random-effects frameworks for objects in metric spaces remain underdeveloped. In this paper, we propose a nonlinear Fr\'echet-based algorithm for random-effects modeling of arbitrary random objects defined on a metric space. Using M-estimation theory, we establish conditions under which the proposed metric-space prediction target is consistently estimated under a working random-effects formulation. We then evaluate the empirical performance of the proposed method using both synthetic data and digital health datasets that require practical tools for analyzing random objects in metric spaces, such as multivariate probability distributions and random graphs. We show that, although our method is developed beyond Hilbert spaces, it can outperform existing Hilbert space-based methods.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a nonlinear Fréchet-based algorithm for random-effects modeling of arbitrary random objects defined on a metric space. It invokes M-estimation theory to establish conditions under which the metric-space prediction target is consistently estimated under a working random-effects formulation. The approach is evaluated empirically on synthetic data and digital health datasets involving multivariate probability distributions and random graphs, with claims that it can outperform existing Hilbert space-based methods.
Significance. If the consistency results hold under the stated technical conditions on the metric space and random objects, the work addresses an important gap by extending mixed-effects modeling beyond Euclidean and Hilbert spaces to general metric spaces. This could enable more efficient estimation and personalized prediction for complex non-Euclidean data types increasingly encountered in applications such as digital health. The conditional framing of the guarantees is appropriate, and the empirical outperformance claim, if substantiated with quantitative comparisons, would strengthen the practical contribution.
major comments (2)
- Abstract: The claim that M-estimation theory is used to establish consistency conditions is central to the theoretical contribution, yet the abstract supplies no explicit conditions, proof sketches, or error bounds. This makes it impossible to assess whether the technical assumptions on the metric space and random objects are verifiable or overly restrictive.
- Empirical section: Claims of outperformance over Hilbert space-based methods are stated without quantitative results, specific metrics, baseline details, or comparison tables. This undermines evaluation of the practical advantage for the central claim that the method works beyond Hilbert spaces.
Simulated Author's Rebuttal
We thank the referee for their constructive comments. We address each major point below and indicate planned revisions.
read point-by-point responses
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Referee: Abstract: The claim that M-estimation theory is used to establish consistency conditions is central to the theoretical contribution, yet the abstract supplies no explicit conditions, proof sketches, or error bounds. This makes it impossible to assess whether the technical assumptions on the metric space and random objects are verifiable or overly restrictive.
Authors: We agree the abstract would benefit from greater specificity on the theoretical contribution. We will revise it to briefly state the key conditions (metric space complete and separable, unique Fréchet mean, finite second moment) and note that consistency follows from standard M-estimation arguments. Full proofs and any quantitative bounds remain in the body of the paper. revision: yes
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Referee: Empirical section: Claims of outperformance over Hilbert space-based methods are stated without quantitative results, specific metrics, baseline details, or comparison tables. This undermines evaluation of the practical advantage for the central claim that the method works beyond Hilbert spaces.
Authors: We acknowledge that the empirical claims require stronger quantitative support. In the revised manuscript we will add explicit performance metrics (e.g., prediction error or MSE), identify the exact Hilbert-space baselines used, and include comparison tables for both the synthetic and digital-health experiments. revision: yes
Circularity Check
No significant circularity; derivation is self-contained
full rationale
The paper proposes a nonlinear Fréchet-based random-effects algorithm for arbitrary random objects in metric spaces and derives consistency of the prediction target via standard M-estimation theory under explicitly stated technical conditions on the metric space and objects. No load-bearing steps reduce by construction to fitted inputs, self-definitions, or unverified self-citations; the consistency claims are conditional on external assumptions rather than tautological. The empirical evaluations on synthetic and digital health data further stand apart from the theoretical derivation. This is the normal case of an independent proposal with standard supporting theory.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
-
[1]
Geodesic Mixed Effects Models for Repeatedly Ob- served/Longitudinal Random Objects
Satarupa Bhattacharjee et al. “Geodesic Mixed Effects Models for Repeatedly Ob- served/Longitudinal Random Objects”. In:Journal of the American Statistical Association 120.551 (2025), pp. 1879–1892.DOI: 10.1080/01621459.2025.2474267. eprint: https: //doi.org/10.1080/01621459.2025.2474267 .URL: https://doi.org/10.1080/ 01621459.2025.2474267
-
[2]
Nonlinear Global Fréchet Regression for Random Objects via Weak Conditional Expectation
Satarupa Bhattacharjee et al. “Nonlinear Global Fréchet Regression for Random Objects via Weak Conditional Expectation”. In:The Annals of Statistics53.1 (2025), pp. 117–143.DOI: 10.1214/24-AOS2457
-
[3]
Single Index Fréchet Regression
Satarupa Bhattacharjee et al. “Single Index Fréchet Regression”. In:The Annals of Statistics 51.4 (2023), pp. 1770–1798.DOI:10.1214/23-AOS2307
-
[4]
Medoid Splits for Efficient Random Forests in Metric Spaces
Matthieu Bulté et al. “Medoid Splits for Efficient Random Forests in Metric Spaces”. In: Computational Statistics & Data Analysis198 (2024), p. 107995.DOI: 10.1016/j.csda. 2024.107995
-
[5]
Han Chen et al. “Sliced Wasserstein Regression”. In:arXiv preprint arXiv:2306.10601(2023). DOI:10.48550/arXiv.2306.10601
-
[6]
Yaqing Chen et al. “Wasserstein Regression”. In:Journal of the American Statistical Associa- tion118.542 (2023), pp. 869–882.DOI:10.1080/01621459.2021.1956937
-
[7]
Crainiceanu et al.Functional Data Analysis with R
C.M. Crainiceanu et al.Functional Data Analysis with R. Chapman and Hall/CRC, 2024
2024
-
[8]
Bootstrap-based inference on the difference in the means of two correlated functional processes
Ciprian M Crainiceanu et al. “Bootstrap-based inference on the difference in the means of two correlated functional processes”. In:Statistics in medicine31.26 (2012), pp. 3223–3240
2012
-
[9]
Fast Univariate Inference for Longitudinal Functional Models
Erjia Cui et al. “Fast Univariate Inference for Longitudinal Functional Models”. In:Journal of Computational and Graphical Statistics0.0 (2021), pp. 1–12.DOI: 10.1080/10618600. 2021.1950006 . eprint: https://doi.org/10.1080/10618600.2021.1950006 .URL: https://doi.org/10.1080/10618600.2021.1950006
-
[10]
Fast univariate inference for longitudinal functional models
Erjia Cui et al. “Fast univariate inference for longitudinal functional models”. In:Journal of Computational and Graphical Statistics(2021), pp. 1–12
2021
-
[11]
Fréchet analysis of variance for random objects
Paromita Dubey et al. “Fréchet analysis of variance for random objects”. In:Biometrika106.4 (2019), pp. 803–821
2019
-
[12]
Paromita Dubey et al. “Modeling Time-Varying Random Objects and Dynamic Networks”. In:Journal of the American Statistical Association117.540 (2022), pp. 2252–2267.DOI: 10.1080/01621459.2021.1917416
-
[13]
Conditional Distribution Regression for Functional Responses
Jianing Fan et al. “Conditional Distribution Regression for Functional Responses”. In:Scandi- navian Journal of Statistics49.2 (2022), pp. 502–524.DOI:10.1111/sjos.12525
-
[14]
Alex Fout et al. “Fréchet Covariance and MANOV A Tests for Random Objects in Multiple Metric Spaces”. In:arXiv preprint arXiv:2306.12066(2023).DOI: 10.48550/arXiv.2306. 12066
-
[15]
Les éléments aléatoires de nature quelconque dans un espace distancié
Maurice Fréchet. “Les éléments aléatoires de nature quelconque dans un espace distancié”. In: Annales de l’institut Henri Poincaré. V ol. 10. 4. 1948, pp. 215–310
1948
-
[16]
Sara A Geer.Empirical Processes in M-estimation. V ol. 6. Cambridge university press, 2000
2000
-
[17]
Cambridge university press, 2007
Andrew Gelman et al.Data analysis using regression and multilevel/hierarchical models. Cambridge university press, 2007
2007
-
[18]
Longitudinal scalar-on-functions regression with application to trac- tography data
Jan Gertheiss et al. “Longitudinal scalar-on-functions regression with application to trac- tography data”. In:Biostatistics14.3 (Jan. 2013), pp. 447–461.ISSN: 1465-4644.DOI: 10. 1093/biostatistics/kxs051. eprint: https://academic.oup.com/biostatistics/ article-pdf/14/3/447/17738955/kxs051.pdf .URL: https://doi.org/10.1093/ biostatistics/kxs051
2013
-
[19]
Aritra Ghosal et al. “Predicting distributional profiles of physical activity in the NHANES database using a Partially Linear Single-Index Fr\’echet Regression model”. In:arXiv preprint arXiv:2302.07692(2023)
-
[20]
Longitudinal functional principal component analysis
Sonja Greven et al. “Longitudinal functional principal component analysis”. eng. In:Electronic journal of statistics4 (2010). 21743825[pmid], pp. 1022–1054.ISSN: 1935-7524.DOI: 10. 1214/10-EJS575.URL:https://pubmed.ncbi.nlm.nih.gov/21743825
-
[21]
Léo Grinsztajn et al. “Why do tree-based models still outperform deep learning on tabular data?” In:arXiv preprint arXiv:2207.08815(2022).DOI: 10.48550/arXiv.2207.08815 . URL:https://doi.org/10.48550/arXiv.2207.08815. 11
-
[22]
Mixed-effects random forest for clustered data
Ahlem Hajjem et al. “Mixed-effects random forest for clustered data”. In:Journal of Statistical Computation and Simulation84.6 (2014), pp. 1313–1328.DOI: 10.1080/00949655.2012. 741599
-
[23]
Universal Bayes Consistency in Metric Spaces
Steve Hanneke et al. “Universal Bayes Consistency in Metric Spaces”. In:The Annals of Statistics49.4 (2021), pp. 2129–2155.DOI:10.1214/20-AOS2029
-
[24]
Locally Polynomial Hilbertian Additive Regression
Jeong Min Jeon et al. “Locally Polynomial Hilbertian Additive Regression”. In:Bernoulli28.3 (2022), pp. 2034–2066.DOI:10.3150/21-BEJ1410
-
[25]
Usable and precise asymptotics for generalized linear mixed model analysis and design
Jiming Jiang et al. “Usable and precise asymptotics for generalized linear mixed model analysis and design”. In:Journal of the Royal Statistical Society Series B: Statistical Methodology84.1 (2022), pp. 55–82
2022
-
[26]
Model Averaging for Global Fréchet Regression
Daisuke Kurisu et al. “Model Averaging for Global Fréchet Regression”. In:Journal of Multivariate Analysis207 (2025), p. 105416.DOI:10.1016/j.jmva.2025.105416
-
[27]
Random-effects models for longitudinal data
Nan M Laird et al. “Random-effects models for longitudinal data”. In:Biometrics(1982), pp. 963–974
1982
-
[28]
Conformal and knn predictive uncertainty quantification algorithms in metric spaces
Gábor Lugosi et al. “Conformal and knn predictive uncertainty quantification algorithms in metric spaces”. In:arXiv preprint arXiv:2507.15741(2025)
-
[29]
Second Errata to “Distance Covariance in Metric Spaces
Russell Lyons. “Second Errata to “Distance Covariance in Metric Spaces””. In:The Annals of Probability49.5 (2021), pp. 2668–2670.DOI:10.1214/20-AOP1504
-
[30]
Application of functional data analysis for the prediction of maxi- mum heart rate
Marcos Matabuena et al. “Application of functional data analysis for the prediction of maxi- mum heart rate”. In:IEEE Access7 (2019), pp. 121841–121852
2019
-
[31]
Beyond scalar metrics: functional data analysis of postprandial continuous glucose monitoring in the AEGIS study
Marcos Matabuena et al. “Beyond scalar metrics: functional data analysis of postprandial continuous glucose monitoring in the AEGIS study”. In:BMC Medical Research Methodology (2026)
2026
-
[32]
Estimating Knee Movement Patterns of Recreational Runners Across Training Sessions Using Multilevel Functional Regression Models
Marcos Matabuena et al. “Estimating Knee Movement Patterns of Recreational Runners Across Training Sessions Using Multilevel Functional Regression Models”. In:The American Statisticianjust-accepted (2022), pp. 1–24
2022
-
[33]
Glucodensities: a new representation of glucose profiles using distributional data analysis
Marcos Matabuena et al. “Glucodensities: a new representation of glucose profiles using distributional data analysis”. In:Statistical Methods in Medical Research30.6 (2021), pp. 1445– 1464
2021
-
[34]
A novel single-crystal & single-pass source for polarisation- and colour-entangled photon pairs,
Marcos Matabuena et al. “Glucodensity functional profiles outperform traditional continuous glucose monitoring metrics”. In:Scientific Reports15.1 (Sept. 29, 2025). Article number: 33662, p. 33662.ISSN: 2045-2322.DOI: 10.1038/s41598- 025- 18119- 2.URL: https: //doi.org/10.1038/s41598-025-18119-2
- [35]
-
[36]
Multilevel functional distributional models with applications to continuous glucose monitoring in diabetes clinical trials
Marcos Matabuena et al. “Multilevel functional distributional models with applications to continuous glucose monitoring in diabetes clinical trials”. In:The Annals of Applied Statistics 20.1 (2026), pp. 476–495
2026
-
[37]
Marcos Matabuena et al. “Personalized Imputation in Metric Spaces via Conformal Prediction: Applications in Predicting Diabetes Development with Continuous Glucose Monitoring Infor- mation”. In:arXiv preprint arXiv:2403.18069(2024).DOI:10.48550/arXiv.2403.18069
-
[38]
WassersteinF -tests and confidence bands for the Fréchet regression of density response curves
Alexander Petersen et al. “WassersteinF -tests and confidence bands for the Fréchet regression of density response curves”. In:The Annals of Statistics49.1 (2021), pp. 590–611
2021
-
[39]
Large sample confidence regions based on subsamples under minimal assumptions
Dimitris N Politis et al. “Large sample confidence regions based on subsamples under minimal assumptions”. In:The Annals of Statistics(1994), pp. 2031–2050
1994
-
[40]
CatBoost: unbiased boosting with categorical features
Liudmila Prokhorenkova et al. “CatBoost: unbiased boosting with categorical features”. In: Advances in Neural Information Processing Systems 31. 2018, pp. 6639–6649.DOI: 10 . 5555/3327757.3327770 .URL: https://papers.nips.cc/paper/7898- catboost- unbiased-boosting-with-categorical-features
-
[41]
Semi-supervised Fréchet Regression
Rui Qiu et al. “Semi-supervised Fréchet Regression”. In:arXiv preprint arXiv:2404.10444 (2024).DOI:10.48550/arXiv.2404.10444
-
[42]
Improving generalised estimating equations using quadratic inference func- tions
Annie Qu et al. “Improving generalised estimating equations using quadratic inference func- tions”. In:Biometrika87.4 (2000), pp. 823–836
2000
-
[43]
Christof Schötz. “Nonparametric Regression in Nonstandard Spaces”. In:Electronic Journal of Statistics16.2 (2022), pp. 4679–4741.DOI:10.1214/22-EJS2056. 12
-
[44]
Gaussian Process Boosting
Fabio Sigrist. “Gaussian Process Boosting”. In:Journal of Machine Learning Research23.232 (2022), pp. 1–46.URL:http://jmlr.org/papers/v23/20-322.html
2022
-
[45]
Continuous Glucose Monitoring and Intensive Treatment of Type 1 Diabetes
W.V . Tamborlane et al. “Continuous Glucose Monitoring and Intensive Treatment of Type 1 Diabetes”. In:New England Journal of Medicine359.14 (2008), pp. 1464–1476
2008
-
[46]
Danielle C. Tucker et al. “Variable Selection for Global Fréchet Regression”. In:Journal of the American Statistical Association118 (2023), pp. 1023–1037.DOI: 10.1080/01621459. 2021.1969240
-
[47]
Journal of the American Statistical Association , author =
Qi Zhang et al. “Dimension Reduction for Fréchet Regression”. In:Journal of the American Statistical Association119.548 (2024), pp. 2733–2747.DOI: 10.1080/01621459.2023. 2277406
-
[48]
Yidong Zhou et al. “Dynamic Network Regression”. In:arXiv preprint arXiv:2109.02981 (2021).DOI:10.48550/arXiv.2109.02981
-
[49]
Network regression with graph Laplacians
Yidong Zhou et al. “Network regression with graph Laplacians”. In:Journal of Machine Learning Research23.320 (2022), pp. 1–41
2022
-
[50]
Alain F Zuur et al.Mixed effects models and extensions in ecology with R. V ol. 574. Springer, 2009. 13
2009
discussion (0)
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