pith. sign in

arxiv: 2510.09028 · v2 · pith:Q5XLNHGPnew · submitted 2025-10-10 · 🧮 math.ST · stat.TH

Drift estimation for rough processes under small noise asymptotic : QMLE approach

Pith reviewed 2026-05-21 20:42 UTC · model grok-4.3

classification 🧮 math.ST stat.TH
keywords volterraalphadrifterrorestimatorfunctionkernelprocess
0
0 comments X

The pith

Constructs QMLE for drift parameter in singular Volterra SDE with small diffusion, proving path reconstruction error O(h^{1/2}) independent of roughness α and yielding efficient estimator as ε→0.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The authors study a stochastic process X^ε defined by a Volterra integral equation whose kernel is singular near zero, behaving like u to the power α-1 where α is between one half and one. This produces rougher sample paths than ordinary Brownian motion. The drift function contains an unknown parameter θ star. The diffusion term is scaled by a small parameter ε that tends to zero. The process is observed only at discrete times separated by a mesh size h that also tends to zero. The central technical step is to invert the Volterra kernel and recover the path of an underlying semimartingale. The paper shows that the reconstruction error is of order square root of h and that this rate holds regardless of the roughness parameter α. With this control on the error, the authors define an explicit contrast function and prove that the resulting quasi-maximum likelihood estimator is efficient in the small-noise limit.

Core claim

We show that this error decreases as h^{1/2} regardless of the value of α. Then, we can introduce an explicit contrast function, which yields an efficient estimator when ε → 0.

Load-bearing premise

The diffusion coefficient is proportional to ε → 0 and the Volterra kernel exhibits singular behavior comparable to K0(u) = c u^{α-1} for α ∈ (1/2,1), with observations at discrete mesh h → 0.

read the original abstract

We consider a process $X^\ve$ solution of a stochastic Volterra equation with an unknown parameter $\theta^\star$ in the drift function. The Volterra kernel is singular near zero, exhibiting a behavior comparable to $K\_0(u)=cu^{\alpha-1} \id{u>0}$ with $\alpha \in (1/2,1)$.It is assumed that the diffusion coefficient is proportional to $\ve \to 0$. Based on discrete observations, with a mesh size $h\to0$, of the Volterra process, we construct a Quasi Maximum Likelihood Estimator. The main step is to assess the error arising in the reconstruction of the path of a semimartingale from the inversion of the Volterra kernel. We show that this error decreases as $h^{1/2}$ regardless of the value of $\alpha$. Then, we can introduce an explicit contrast function, which yields an efficient estimator when $\ve \to 0$.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper considers drift parameter estimation for the solution X^ε of a stochastic Volterra equation with singular kernel behaving as K_0(u) ∼ u^{α-1} for α ∈ (1/2,1), under small-noise asymptotics where the diffusion coefficient scales with ε → 0. Discrete observations at mesh h → 0 are used to construct a quasi-maximum likelihood estimator (QMLE). The central technical step is to bound the reconstruction error of the driving semimartingale path obtained by inverting the Volterra kernel; the authors claim this error is O(h^{1/2}) uniformly in α. An explicit contrast function is then introduced whose minimizer is asserted to be asymptotically efficient as ε → 0.

Significance. If the uniform-in-α reconstruction bound is established rigorously, the result would be significant for extending QMLE methods to rough Volterra processes observed discretely in the small-noise regime. The explicit contrast function and the claimed independence of the error rate from the roughness parameter α constitute concrete strengths that could facilitate applications in rough volatility and fractional stochastic models.

major comments (2)
  1. [Abstract / reconstruction analysis] Abstract and the main reconstruction step: the assertion that the error in recovering the driving semimartingale via inversion of the singular kernel K_0(u) ∼ u^{α-1} is O(h^{1/2}) uniformly for α ∈ (1/2,1) is load-bearing for the efficiency claim. Because the inverse Volterra operator becomes increasingly ill-conditioned as α ↓ 1/2, the discretization error at scale h may be amplified by a factor that diverges with α; the proof must exhibit an explicit constant independent of α (or quantify any logarithmic divergence) to justify the subsequent contrast function and efficiency result.
  2. [Contrast function and efficiency] Section introducing the contrast function (following the reconstruction): the derivation of asymptotic efficiency as ε → 0 must explicitly track how the O(h^{1/2}) reconstruction error propagates into the contrast and its minimizer. Any joint regime between h and ε should be stated, together with the precise sense in which efficiency holds (e.g., asymptotic normality with the information bound).
minor comments (2)
  1. [Model setup] The precise form of the diffusion coefficient (proportional to ε) and the exact definition of the Volterra kernel should be restated in the model section with all constants made explicit.
  2. [Introduction] A short discussion of related literature on discrete observations of Volterra or rough processes would improve context.

Simulated Author's Rebuttal

2 responses · 0 unresolved

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 to strengthen the presentation of the uniformity in the reconstruction bound and the error propagation analysis.

read point-by-point responses
  1. Referee: [Abstract / reconstruction analysis] Abstract and the main reconstruction step: the assertion that the error in recovering the driving semimartingale via inversion of the singular kernel K_0(u) ∼ u^{α-1} is O(h^{1/2}) uniformly for α ∈ (1/2,1) is load-bearing for the efficiency claim. Because the inverse Volterra operator becomes increasingly ill-conditioned as α ↓ 1/2, the discretization error at scale h may be amplified by a factor that diverges with α; the proof must exhibit an explicit constant independent of α (or quantify any logarithmic divergence) to justify the subsequent contrast function and efficiency result.

    Authors: We thank the referee for highlighting this point. In the proof of the reconstruction error (Section 3), the O(h^{1/2}) bound is obtained via a fractional integral representation of the inverse Volterra operator. The resulting constant is independent of α ∈ (1/2,1) because the estimates rely on uniform bounds for the singular kernel inversion that do not deteriorate as α approaches 1/2. We will revise the manuscript to display the explicit constant and add a remark confirming its α-independence, thereby addressing the concern about possible ill-conditioning. revision: yes

  2. Referee: [Contrast function and efficiency] Section introducing the contrast function (following the reconstruction): the derivation of asymptotic efficiency as ε → 0 must explicitly track how the O(h^{1/2}) reconstruction error propagates into the contrast and its minimizer. Any joint regime between h and ε should be stated, together with the precise sense in which efficiency holds (e.g., asymptotic normality with the information bound).

    Authors: We agree that a more explicit tracking of the reconstruction error through the contrast function improves clarity. The O(h^{1/2}) term enters the contrast as an additive perturbation whose contribution vanishes in the small-noise limit ε → 0 provided h satisfies a suitable relation to ε (e.g., h = o(ε^2)). We will revise the relevant section to derive this propagation step by step and state the joint asymptotic regime under which the QMLE is asymptotically normal and attains the information bound. revision: yes

Circularity Check

0 steps flagged

Derivation proceeds from explicit error bound to contrast without reduction to inputs

full rationale

The paper establishes a reconstruction error bound of order h^{1/2} for recovering the semimartingale path via Volterra kernel inversion from discrete observations, then uses this bound to define an explicit contrast function whose minimizer is shown to be efficient as ε→0. This chain supplies independent content: the error bound is derived from the kernel singularity and mesh properties rather than presupposing the estimator's efficiency, and the contrast is constructed explicitly rather than fitted to the target quantity. No self-definitional loop, fitted input renamed as prediction, or load-bearing self-citation chain is present in the provided derivation steps. The result is therefore self-contained against external benchmarks for the small-noise asymptotic.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The paper rests on standard existence results for stochastic Volterra equations and the given singular kernel form; the parameter θ* is the object of estimation rather than a fitted constant introduced by the authors.

free parameters (1)
  • θ*
    Unknown parameter inside the drift function; the target of the QMLE rather than an ad-hoc constant chosen to close a derivation.
axioms (2)
  • standard math The stochastic Volterra equation admits a unique solution X^ε.
    Invoked to define the observed process.
  • domain assumption The Volterra kernel is singular near zero with behavior comparable to c u^{α-1} for α ∈ (1/2,1).
    Stated in the model setup and used to control the inversion error.

pith-pipeline@v0.9.0 · 5701 in / 1444 out tokens · 35889 ms · 2026-05-21T20:42:29.588617+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

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

40 extracted references · 40 canonical work pages · 2 internal anchors

  1. [1]

    Affine Vo lterra Processes

    Eduardo Abi Jaber, Martin Larsson, and Sergio Pulido. “Affine Vo lterra Processes”. In: The Annals of Applied Probability 29.5 (Oct. 1, 2019). issn: 1050-5164. doi: 10.1214/19-AAP1477. url: https://projecteuclid.org/journals/annals-of-appli

  2. [2]

    A Perspective on the Numerical Trea tment of Volterra Equations

    Christopher T. H. Baker. “A Perspective on the Numerical Trea tment of Volterra Equations”. In: Journal of Computational and Applied Mathe- matics. Numerical Analysis 2000. Vol. VI: Ordinary Differential Equations and Integral Equations 125.1 (Dec. 15, 2000), pp. 217–249. issn: 0377-

  3. [3]

    url: https://www.sciencedirect.com/science/article

    doi: 10.1016/S0377-0427(00)00470-2. url: https://www.sciencedirect.com/science/article

  4. [4]

    Modelling Energy Spot Prices by Volatility Modulated L´ evy-driven Volterra Processes

    Ole E. Barndorff-Nielsen, Fred Espen Benth, and Almut E. D. Vera art. “Modelling Energy Spot Prices by Volatility Modulated L´ evy-driven Volterra Processes”. In: Bernoulli 19.3 (Aug. 2013), pp. 803–845. issn: 1350-7265. doi: 10.3150/12-BEJ476. url: https://projecteuclid.org/journals/bernoulli/volume-19/issue- 29 Table 1: α = 0. 8, ( θ0, θ 1) = ( − 1, 1), ...

  5. [5]

    Volterra Equations with Itˆ o Inte- grals—I

    Marc A. Berger and Victor J. Mizel. “Volterra Equations with Itˆ o Inte- grals—I”. In: Journal of Integral Equations 2.3 (1980), pp. 187–245. issn: 0163-5549. JSTOR: 26164035. url: https://www.jstor.org/stable/26164035

  6. [6]

    Volterra Equations with Itˆ o Inte- grals—II

    Marc A. Berger and Victor J. Mizel. “Volterra Equations with Itˆ o Inte- grals—II”. In: Journal of Integral Equations 2.4 (1980), pp. 319–337. issn: 0163-5549. JSTOR: 26164044. url: https://www.jstor.org/stable/26164044

  7. [7]

    The Pie cewise Polynomial Collocation Method for Nonlinear Weakly Singular Volterra Equations

    Hermann Brunner, Arvet Pedas, and Gennadi Vainikko. “The Pie cewise Polynomial Collocation Method for Nonlinear Weakly Singular Volterra Equations”. In: Mathematics of Computation 68.227 (Feb. 8, 1999), pp. 1079–

  8. [8]

    doi: 10.1090/s0025-5718-99-01073-x

    issn: 0025-5718, 1088-6842. doi: 10.1090/s0025-5718-99-01073-x . url: https://www.ams.org/mcom/1999-68-227/S0025-5718-99- 01073-X/

  9. [9]

    Statistical Inference for Rough Volat ility: Central Limit Theorems

    Carsten H. Chong et al. “Statistical Inference for Rough Volat ility: Central Limit Theorems”. In: The Annals of Applied Probability 34.3 (June 2024), pp. 2600–2649. issn: 1050-5164, 2168-8737. doi: 10.1214/23-AAP2002. url: https://projecteuclid.org/journals/annals-of-applie d-probability/volume-34/issue-3/

  10. [10]

    Statistical Inference for Rough Volat ility: Min- imax Theory

    Carsten H. Chong et al. “Statistical Inference for Rough Volat ility: Min- imax Theory”. In: The Annals of Statistics 52.4 (Aug. 2024), pp. 1277–

  11. [11]

    doi: 10.1214/23-AOS2343

    issn: 0090-5364, 2168-8966. doi: 10.1214/23-AOS2343. url: https://projecteuclid.org/journa

  12. [12]

    S tochastic Volterra Equations with Singular Kernels

    W. George Cochran, Jung-Soon Lee, and J¨ urgen Potthoff. “S tochastic Volterra Equations with Singular Kernels”. In: Stochastic Processes and their Applications 56.2 (Apr. 1, 1995), pp. 337–349. issn: 0304-4149. doi: 10.1016/0304-4149(94)00072-2 . url: https://www.sciencedirect.com/science/article/pii/030441

  13. [13]

    Roughen ing Hes- ton

    Omar El Euch, Jim Gatheral, and Mathieu Rosenbaum. “Roughen ing Hes- ton”. In: SSRN Electronic Journal (2018). issn: 1556-5068. doi: 10.2139/ssrn.3116887. url: https://www.ssrn.com/abstract=3116887

  14. [14]

    The characteristic function of rough Heston models

    Omar El Euch and Mathieu Rosenbaum. The Characteristic Function of Rough Heston Models . Sept. 7, 2016. arXiv: 1609.02108 [q-fin] . url: http://arxiv.org/abs/1609.02108. Pre-published

  15. [15]

    Identification of Dynamical Sys- tems with Small Noise

    given-i=Yu family=Kutoyants given=Yu. Identification of Dynamical Sys- tems with Small Noise . Dordrecht: Springer Netherlands, 1994. isbn: 978- 94-010-4444-8 978-94-011-1020-4. doi: 10.1007/978-94-011-1020-4 . url: http://link.springer.com/10.1007/978-94-011-1020-4

  16. [16]

    Con- sistent Estimation for Fractional Stochastic Volatility Model under High- Frequency Asymptotics

    Masaaki Fukasawa, Tetsuya Takabatake, and Rebecca West phal. “Con- sistent Estimation for Fractional Stochastic Volatility Model under High- Frequency Asymptotics”. In: Mathematical Finance 32.4 (2022), pp. 1086–

  17. [17]

    doi: 10.1111/mafi.12354

    issn: 1467-9965. doi: 10.1111/mafi.12354. url: https://onlinelibrary.wiley.com/doi/abs/10

  18. [18]

    , Jaisson, T

    Jim Gatheral, Thibault Jaisson, and Mathieu Rosenbaum. “Volatilit y Is Rough”. In: Quantitative Finance 18.6 (June 3, 2018), pp. 933–949. issn: 1469-7688, 1469-7696. doi: 10.1080/14697688.2017.1393551. url: https://www.tandfonline.com/doi/

  19. [19]

    The Quadratic Rough Heston Model and the Joint S&P 500/VIX Smile Calibrati on Prob- lem

    Jim Gatheral, Paul Jusselin, and Mathieu Rosenbaum. The Quadratic Rough Heston Model and the Joint S&P 500/VIX Smile Calibrati on Prob- lem. Jan. 6, 2020. arXiv: 2001.01789 [q-fin] . url: http://arxiv.org/abs/2001.01789. Pre-published. 34

  20. [20]

    On the estimation of the diffu- sion coefficient for multi-dimensional diffusion processes

    Valentine Genon-Catalot and Jean Jacod. “On the estimation of the diffu- sion coefficient for multi-dimensional diffusion processes”. In: Annales de l’I.H.P. Probabilit´ es et statistiques 29.1 (1993), pp. 119–151. issn: 1778-

  21. [21]

    url: http://www.numdam.org/item/AIHPB_1993__29_1_119_0/

  22. [22]

    Parametric Inference for Small Variance and Long Time Horizon McKean-Vlasov Diffusion Mod- els

    Valentine Genon-Catalot and Catherine Lar´ edo. “Parametric Inference for Small Variance and Long Time Horizon McKean-Vlasov Diffusion Mod- els”. In: Electronic Journal of Statistics 15.2 (Jan. 2021), pp. 5811–5854. issn: 1935-7524, 1935-7524. doi: 10.1214/21-EJS1922. url: https://projecteuclid.org/journals/el

  23. [23]

    Drift Estimation for Rough Pro- cesses under Small Noise Asymptotic: Trajectory Fitting Me thod

    Arnaud Gloter and Nakahiro Yoshida. Drift Estimation for Rough Pro- cesses under Small Noise Asymptotic: Trajectory Fitting Me thod. Mar. 5,

  24. [24]

    Drift estimation for rough processes under small noise asymptotic : trajectory fitting method

    doi: 10.48550/arXiv.2503.03347. arXiv: 2503.03347 [math] . url: http://arxiv.org/abs/2503.03347. Pre-published

  25. [25]

    Parame tric Infer- ence for Discretely Observed Multidimensional Diffusions with Small Dif - fusion Coefficient

    Romain Guy, Catherine Lar´ edo, and Elisabeta Vergu. “Parame tric Infer- ence for Discretely Observed Multidimensional Diffusions with Small Dif - fusion Coefficient”. In: Stochastic Processes and their Applications 124.1 (Jan. 1, 2014), pp. 51–80. issn: 0304-4149. doi: 10.1016/j.spa.2013.07.009. url: https://www.sciencedirect.com/science/article/pii/S030441...

  26. [26]

    Parameter Estimation for a Class of Stochastic Differ- ential Equations Driven by Small Stable Noises from Discrete Observ a- tions

    Long Hongwei. “Parameter Estimation for a Class of Stochastic Differ- ential Equations Driven by Small Stable Noises from Discrete Observ a- tions”. In: Acta Mathematica Scientia 30.3 (May 2010), pp. 645–663. issn: 02529602. doi: 10.1016/S0252-9602(10)60067-7. url: https://linkinghub.elsevier.com/retrieve

  27. [27]

    Well-Posedn ess and Regularity for Solutions of Caputo Stochastic Fractional Differential Equa- tions in Lp Spaces

    Phan Thi Huong, P.E. Kloeden, and Doan Thai Son. “Well-Posedn ess and Regularity for Solutions of Caputo Stochastic Fractional Differential Equa- tions in Lp Spaces”. In: Stochastic Analysis and Applications 41.1 (Jan. 2, 2023), pp. 1–15. issn: 0736-2994. doi: 10.1080/07362994.2021.1988856. url: https://doi.org/10.1080/07362994.2021.1988856

  28. [28]

    A New Smoothness Res ult for Caputo-type Fractional Ordinary Differential Equations

    Binjie Li, Xiaoping Xie, and Shiquan Zhang. “A New Smoothness Res ult for Caputo-type Fractional Ordinary Differential Equations”. In : Applied Mathematics and Computation 349 (May 15, 2019), pp. 408–420. issn: 0096-3003. doi: 10.1016/j.amc.2018.12.052. url: https://www.sciencedirect.com/science/article

  29. [29]

    Volterra Equations Driven by Semimartingales

    Philip Protter. “Volterra Equations Driven by Semimartingales”. In: The Annals of Probability 13.2 (May 1985), pp. 519–530. issn: 0091-1798, 2168- 894X. doi: 10.1214/aop/1176993006. url: https://projecteuclid.org/journals/annals-of-probab

  30. [30]

    Philip E. Protter. Stochastic Integration and Differential Equations. Vol. 21. Stochastic Modelling and Applied Probability. Berlin, Heidelberg: Spring er Berlin Heidelberg, 2005. isbn: 978-3-642-05560-7 978-3-662-10061-5. doi: 10.1007/978-3-662-10061-5 . url: http://link.springer.com/10.1007/978-3-662-10061-5

  31. [31]

    Pr¨ omel and David Scheffels

    David J. Pr¨ omel and David Scheffels. Stochastic Volterra Equations with H¨ older Diffusion Coefficients. Mar. 28, 2023. doi: 10.48550/arXiv.2204.02648. arXiv: 2204.02648. url: http://arxiv.org/abs/2204.02648. Pre-published. 35

  32. [32]

    Paracontrolled Distribut ion Ap- proach to Stochastic Volterra Equations

    David J. Pr¨ omel and Mathias Trabs. “Paracontrolled Distribut ion Ap- proach to Stochastic Volterra Equations”. In: Journal of Differential Equa- tions 302 (Nov. 2021), pp. 222–272. issn: 00220396. doi: 10.1016/j.jde.2021.08.031. url: https://linkinghub.elsevier.com/retrieve/pii/S0022039621005428

  33. [33]

    Discrete-Time Sim u- lation of Stochastic Volterra Equations

    Alexandre Richard, Xiaolu Tan, and Fan Yang. “Discrete-Time Sim u- lation of Stochastic Volterra Equations”. In: Stochastic Processes and their Applications 141 (Nov. 1, 2021), pp. 109–138. issn: 0304-4149. doi: 10.1016/j.spa.2021.07.003. url: https://www.sciencedirect.com/science/article/pii/S0304414

  34. [34]

    Small-Diffusion Asympt otics for Discretely Sampled Stochastic Differential Equations

    Michael Sørensen and Masayuki Uchida. “Small-Diffusion Asympt otics for Discretely Sampled Stochastic Differential Equations”. In: Bernoulli 9.6 (Dec. 2003), pp. 1051–1069. issn: 1350-7265. doi: 10.3150/bj/1072215200. url: https://projecteuclid.org/journals/bernoulli/volume-9/issue-6/Small-diffusion-asymp

  35. [35]

    Information Criteria f or Small Diffusions via the Theory of Malliavin–Watanabe

    Masayuki Uchida and Nakahiro Yoshida. “Information Criteria f or Small Diffusions via the Theory of Malliavin–Watanabe”. In: Statistical Infer- ence for Stochastic Processes 7.1 (Mar. 1, 2004), pp. 35–67. issn: 1572-

  36. [36]

    url: https://doi.org/10.1023/B:SISP.00000164

    doi: 10.1023/B:SISP.0000016462.43348.8f. url: https://doi.org/10.1023/B:SISP.00000164

  37. [37]

    Asymptotic B ehav- ior of Stochastic Lattice Systems with a Caputo Fractional Time Der iva- tive

    Yejuan Wang, Jiaohui Xu, and Peter E. Kloeden. “Asymptotic B ehav- ior of Stochastic Lattice Systems with a Caputo Fractional Time Der iva- tive”. In: Nonlinear Analysis: Theory, Methods & Applications 135 (Apr. 2016), pp. 205–222. issn: 0362546X. doi: 10.1016/j.na.2016.01.020. url: https://linkinghub.elsevier.com/retrieve/pii/S0362546X16000298

  38. [38]

    Existence and Uniqueness of Solutions to Stoch astic Volterra Equations with Singular Kernels and Non-Lipschitz Coefficien ts

    Zhidong Wang. “Existence and Uniqueness of Solutions to Stoch astic Volterra Equations with Singular Kernels and Non-Lipschitz Coefficien ts”. In: Statistics & Probability Letters 78.9 (July 2008), pp. 1062–1071. issn: 01677152. doi: 10.1016/j.spl.2007.10.007. url: https://linkinghub.elsevier.com/retrieve/pii/S

  39. [39]

    Stochastic Volterra equations in Banach spaces and stochastic partial differential equation.J

    Xicheng Zhang. “Stochastic Volterra Equations in Banach Spac es and Stochastic Partial Differential Equation”. In: Journal of Functional Analy- sis 258.4 (Feb. 2010), pp. 1361–1425. issn: 00221236. doi: 10.1016/j.jfa.2009.11.006. url: https://linkinghub.elsevier.com/retrieve/pii/S0022123609004650

  40. [40]

    Volterra Processes and Applications in Financ e

    Elizabeth Zuniga. “Volterra Processes and Applications in Financ e”. PhD thesis. Universit´ e Paris-Saclay, June 17, 2021.url: https://theses.hal.science/tel-03407166. 36 Table 9: α = 0. 6, ( θ0, θ 1) = ( − 1, 1), T = 50, h = 2 ∗ 10− 2 ∆ ε 1/10 1/20 1/100 1/5 mean (-0.89, 0.90) (-0.85, 0.86) (-0.78, 0.79) (k=10) resc. std. ∗ (1.3, 1.2) (1.1, 0.97) (0.79, ...