REVIEW 3 major objections 3 minor 25 references
VARSHAP: Addressing Global Dependency Problems in Explainable AI with Variance-Based Local Feature Attribution
T0 review · 3 major / 3 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read The paper proposes VARSHAP, a Shapley-based attribution method in which a feature's local importance is the amount by which fixing its value reduces the variance of the model's prediction around the explained instance.
desk verdict Interesting local variance-based Shapley idea, but the central definition is self-contradictory (Eq. 1 vs. Appendix A.3), as the stress-test note correctly identifies. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the variance game $v(S) = \mathrm{Var}_{\Omega}(S)$, evaluated under a local Gaussian perturbation $\Pi(x) = \mathcal{N}(x, \mathrm{diag}(\alpha \hat{\sigma}_i^2))$ centered on the explained instance, with $\alpha$ controlling the size of the neighborhood. The Shapley kernel $\omega(|S|) = |S|!(k - |S| - 1)! / k!$ averages the marginal variance reductions over all coalitions, converting many local perturbation samples into a single axiom-compatible attribution vector.
What would settle it
On a synthetic dataset where $X_2 = X_1 + \text{noise}$ and $Y$ depends only on $X_1$, compute VARSHAP attributions with the diagonal Gaussian perturbation: any substantial nonzero attribution to $X_2$ would show that the independent-perturbation game is not modeling the real feature relationships at the explained point.
Extended reading notes
Core claim
The central claim is that a feature matters locally to the extent that knowing its value reduces the variance of the model output when all other out-of-coalition features are perturbed around the explained instance. Formally, VARSHAP defines the attribution for feature $j$ as $\Phi_j(\Omega, \Pi, x) = \sum_{S \subseteq F \setminus \{j\}} \omega(|S|)\,(\mathrm{Var}_{\Omega}(S \cup \{j\}) - \mathrm{Var}_{\Omega}(S))$, where $\mathrm{Var}_{\Omega}(S)$ is the output variance under the local perturbation distribution with features in $S$ fixed. Because this is a Shapley value of the variance game, it satisfies efficiency, symmetry, and the null-player property, and for additive models the attribution of feature $i$ collapses to $w_i^2 \mathrm{Var}(X_i)$. The paper further proves, under axioms of shift invariance, sign independence, and additivity, that the squared deviation is the unique attribution function, which it presents as the theoretical justification for variance-based local importance.
Load-bearing premise
The method assumes that independent Gaussian noise scaled by each feature's global variance, centered on the explained point, faithfully represents the local neighborhood; if the true local structure is correlated, skewed, or non-Gaussian, the variance reductions are computed over unrealistic points and the attributions may mislead.
Editorial extensions
If this is right
- Explanations for a fixed instance stay stable when the global data distribution changes far away, because only the local perturbation matters.
- The attributions inherit Shapley's efficiency, symmetry, and null-player guarantees, including zero importance for features that do not affect local output variance.
- For additive models, VARSHAP exactly recovers $w_i^2 \mathrm{Var}(X_i)$, giving a closed-form interpretation of attribution as each feature's share of output variance.
- On the benchmark suite, VARSHAP with $\sigma = 0.6$ and $\sigma = 1.0$ ranks first among all compared methods, ahead of KernelSHAP and all LIME variants.
- The uniqueness proof positions variance not as one heuristic choice, but as the only shift-invariant, sign-independent, additive dispersion measure with $d(1) = 1$.
Reading between the lines
- Inference: replacing the diagonal Gaussian with a learned manifold or conditional perturbation would likely extend the same variance-Shapley machinery to correlated features, a direction the paper lists as future work.
- Inference: the variance-reduction view suggests a direct calibration test: compare VARSHAP attributions to actual leave-one-feature-out variance drops at the explained point; the paper does not run this exact check.
- Inference: for classification, output variance could be replaced by predictive entropy or interval width, yielding a variance-analog for non-regression targets.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes VARSHAP, a model-agnostic local feature attribution method that defines the characteristic function of the Shapley game as the variance of the model output under local Gaussian perturbations of out-of-coalition features, with perturbation scale tied to the instance and global per-feature variances. The authors claim that the resulting attributions satisfy the Shapley axioms, are shift-invariant, are resilient to global distribution shifts, and outperform KernelSHAP and LIME on synthetic and benchmark tasks. The appendix provides an axiomatic derivation of variance as the unique local dispersion measure and a linearity result for additive models.
Significance. The local-variance-reduction viewpoint is a reasonable and potentially useful alternative to expectation-based SHAP, and if the consistency issues were resolved, the method could be a meaningful contribution to local XAI. The paper deserves credit for identifying a concrete failure mode of SHAP in the synthetic case studies and for evaluating the method with standard faithfulness, robustness, and complexity metrics. However, as written, the central definition is internally inconsistent, so the claimed theoretical guarantees and experimental results are not currently verifiable.
major comments (3)
- [§2.3, Eq. (1); Appendix A.3, Eq. (36)] Equation (1) defines Φ_j = Σ_S ω(|S|)(Var(S∪{j}) − Var(S)), while Eq. (36) in Appendix A.3 defines Φ_j = Σ_S ω(|S|)(Var(S) − Var(S∪{j})). These are opposite definitions of the same quantity. The surrounding text is also split: §2.3 states that for a linear model the attribution is precisely −w_i² Var(X_i^Π), whereas A.3 Eq. (45) derives +w_j² Var(X_j). In the same section, the efficiency bullet says the sum of attributions equals Var(F)−Var(∅)=−Var(∅), yet it describes this as the total change in variance from the unknown state to the known state, which would have the opposite sign. Because the implemented sign cannot be inferred from the manuscript, the efficiency statement, the case-study interpretations, and the benchmark comparisons are not well-defined. The authors must adopt a single consistent convention, then update all prose, equations, and experimental claims accordingly.
- [Appendix A.2, Proposition 1 and Theorem 1] The claimed uniqueness of variance is conditional on assumptions that essentially build variance into the result. The proof assumes from the outset that the characteristic function has the form v(S)=E[d(Ω−E[Ω])] and imposes the additivity axiom E[d(A+B)] = E[d(A)] + E[d(B)] for independent random variables A and B. The latter axiom is precisely the property that variance satisfies, so the theorem shows that among even, continuous, normalized, and additive dispersion functionals of centered outputs, the only choice is d(x)=x². It does not independently justify variance as the unique attribution metric from more basic desiderata. The manuscript should present these conditions as explicit definitional choices rather than as an independent axiomatic derivation.
- [Section 4, Tables 1 and 2] The aggregated ranking in Table 1 is the main evidence for the claimed superiority, but the differences between VARSHAP (σ=0.6 and σ=1.0) and KernelShap (data sampling) are small, no confidence intervals or significance tests are reported, and the text says metric hyperparameters were 'fine-tuned to ensure an appropriate distribution of scores' (Section 4 and Appendix A.6). The ranking procedure is therefore not transparent enough to support a strong superiority claim. In addition, the perturbation scale σ is a configuration choice of VARSHAP; the paper should justify the selected values or demonstrate stability across a range rather than selecting them from the same benchmarks used for evaluation.
minor comments (3)
- [Section 5] The limitation that independent Gaussian perturbations may not capture complex feature interactions is acknowledged, but because this assumption is load-bearing for the locality claim, the manuscript should explain more explicitly how it affects the synthetic and benchmark conclusions rather than leaving it only as future work.
- [Section 3.1, Figures 1 and 2] The stability claims about VARSHAP and LIME in Case Study 1 are based on visual inspection of normalized attribution bars; providing numerical attribution values or a quantitative similarity measure would make the comparison verifiable.
- [Notation and proofreading] There are several presentation issues: Figure 8's caption contains the typo 'moel', Table 2 repeats 'V ARSHAP (σ=0.6σ= 0.6σ=0.6)', Eq. (1) says 'k total features' while Appendix A.3 uses |F| for the same quantity, and the proof of Theorem 1 switches notation from d to f without explanation. A careful proofread and notation harmonization are needed.
Circularity Check
No circularity: VARSHAP's derivation is an internal axiomatic characterization; the paper's sign inconsistency is a correctness defect, not a circular step.
full rationale
VARSHAP's derivation is self-contained in the circularity sense. Equation (1) explicitly defines the attribution as a Shapley value of the game v(S)=Var_Omega(S), so the claimed efficiency, symmetry, and null-player properties follow by construction from Shapley's theorem rather than by importing an unverified or self-cited result. Appendix A.2 contains a genuine functional-equation argument: from d(0)=0, d(-x)=d(x), E[d(A+B)]=E[d(A)]+E[d(B)] for independent zero-mean A,B, and d(1)=1, the proof derives d(x)=x^2. The additivity axiom is strong and can be viewed as chosen so that variance emerges, but the proof does not assume the conclusion, so this is a characterization theorem, not a circular reduction. The paper contains no self-citations; the impossibility result of Bilodeau et al. is external, and the benchmark comparisons are external and report the tested hyperparameter variants rather than hiding a fitted parameter. The serious defect is internal consistency, not circularity: Section 2.3 Eq. (1) defines Phi_j = sum omega(|S|)(Var(S union {j}) - Var(S)), while Appendix A.3 Eq. (36) defines the same quantity with the opposite sign, Var(S) - Var(S union {j}), and derives Phi_j = Var(Omega_j(X_j)) >= 0; Section 2.3 separately states that the linear-model attribution is exactly -w_i^2 Var(X_i). The abstract's 'variance reduction' narrative is therefore true only for one of the two definitions, and the method is undefined as written. That is a correctness/consistency flaw to be fixed, not an equivalence-by-construction or self-citation chain; hence the circularity score is 0.
Assumptions & free parameters
free parameters (2)
- perturbation scale α/σ =
σ = 0.3, 0.6, 1.0; best at 0.6 and 1.0
- evaluation metric hyperparameters =
subset size 6, Lipschitz std 0.2, MaxSensitivity bound 0.02, EffectiveComplexity epsilon 0.05
assumptions (5)
- ad hoc to paper Additivity for independent random variables: E[d(A+B)] = E[d(A)] + E[d(B)]
- ad hoc to paper The characteristic function v has the form E[d(Ω(x_S, X_{-S}) - E[Ω])]
- domain assumption Zero property and sign independence for d
- domain assumption Gaussian perturbation with diagonal covariance and E[X] = x
- standard math Shapley axioms: efficiency, symmetry, null player, additivity
Cite this review
Pith. "Pith review of VARSHAP: Addressing Global Dependency Problems in Explainable AI with Variance-Based Local Feature Attribution." pith.science (2026). https://pith.science/paper/E4LHN26H
@misc{pith2026250607229,
author = {Pith},
title = {Pith review of: VARSHAP: Addressing Global Dependency Problems in Explainable AI with Variance-Based Local Feature Attribution},
year = {2026},
howpublished = {\url{https://pith.science/paper/E4LHN26H}},
note = {Machine review of arXiv:2506.07229}
}
read the original abstract
Existing feature attribution methods like SHAP often suffer from global dependence, failing to capture true local model behavior. This paper introduces VARSHAP, a novel model-agnostic local feature attribution method which uses the reduction of prediction variance as the key importance metric of features. Building upon Shapley value framework, VARSHAP satisfies the key Shapley axioms, but, unlike SHAP, is resilient to global data distribution shifts. Experiments on synthetic and real-world datasets demonstrate that VARSHAP outperforms popular methods such as KernelSHAP or LIME, both quantitatively and qualitatively.
Figures
Figures from the paper (4 more)
Reference graph
Works this paper leans on
-
[1]
C. Agarwal, N. Johnson, M. Pawelczyk, S. Krishna, E. Saxena, M. Zitnik, and H. Lakkaraju. Rethinking stability for attribution-based explanations.arXiv preprint arXiv:2203.06877, 2022
arXiv 2022
-
[2]
D. Alvarez Melis and T. Jaakkola. Towards robust interpretability with self-explaining neural networks. InAdvances in Neural Information Processing Systems, volume 31, 2018
work page 2018
-
[3]
U. Bhatt, A. Weller, and J. M. Moura. Evaluating and aggregating feature-based model ex- planations. InProceedings of the Twenty-Ninth International Joint Conference on Artificial Intelligence, pages 3016–3022. International Joint Conferences on Artificial Intelligence Or- ganization, 2020
work page 2020
-
[4]
B. Bilodeau, N. Jaques, P. W. Koh, and B. Kim. Impossibility theorems for feature attribution. Proceedings of the National Academy of Sciences, 121(2):e2304406120, 2024
work page 2024
-
[5]
P. Chalasani, J. Chen, A. R. Chowdhury, X. Wu, and S. Jha. Concise explanations of neural networks using adversarial training. InProceedings of the 37th International Conference on Machine Learning, pages 1383–1391. PMLR, 2020
work page 2020
- [6]
-
[7]
R. Guidotti, A. Monreale, S. Ruggieri, F. Turini, F. Giannotti, and D. Pedreschi. A survey of methods for explaining black box models.ACM computing surveys (CSUR), 51(5):1–42, 2018
work page 2018
-
[8]
A. Holzinger, A. Saranti, C. Molnar, P. Biecek, and W. Samek. Explainable ai methods-a brief overview. InInternational workshop on extending explainable AI beyond deep models and classifiers, pages 13–38. Springer, 2020
work page 2020
Show all 25 references
-
[9]
Janzing, L
D. Janzing, L. Minorics, and P. Blöbaum. Feature relevance quantification in explainable ai: A causal problem. InInternational Conference on artificial intelligence and statistics, pages 2907–2916. PMLR, 2020
2020
-
[10]
D. P. Kingma. Adam: A method for stochastic optimization.arXiv preprint arXiv:1412.6980, 2014
2014 arXiv
-
[11]
Klein, C
L. Klein, C. Lüth, U. Schlegel, T. Bungert, M. El-Assady, and P. Jäger. Navigating the maze of explainable ai: A systematic approach to evaluating methods and metrics.Advances in Neural Information Processing Systems, 37:67106–67146, 2024
2024
-
[12]
M. Li, H. Sun, Y . Huang, and H. Chen. Shapley value: from cooperative game to explainable artificial intelligence.Autonomous Intelligent Systems, 4(1):2, 2024
2024
-
[13]
S. M. Lundberg and S.-I. Lee. A unified approach to interpreting model predictions.Advances in Neural Information Processing Systems, 30:4765–4774, 2017. 10
2017
-
[14]
W. J. Murdoch, C. Singh, K. Kumbier, R. Abbasi-Asl, and B. Yu. Definitions, methods, and ap- plications in interpretable machine learning.Proceedings of the National Academy of Sciences, 116(44):22071–22080, 2019
2019
-
[15]
Nguyen and M
A.-p. Nguyen and M. R. Martínez. On quantitative aspects of model interpretability.arXiv preprint arXiv:2007.07584, 2020
2007 arXiv
-
[16]
Pedregosa, G
F. Pedregosa, G. Varoquaux, A. Gramfort, V . Michel, B. Thirion, O. Grisel, M. Blondel, P. Pret- tenhofer, R. Weiss, V . Dubourg, et al. Scikit-learn: Machine learning in Python.Journal of Machine Learning Research, 12:2825–2830, 2011
2011
-
[17]
why should i trust you?
M. T. Ribeiro, S. Singh, and C. Guestrin. " why should i trust you?" explaining the predic- tions of any classifier. InProceedings of the 22nd ACM SIGKDD international conference on knowledge discovery and data mining, pages 1135–1144, 2016
2016
-
[18]
why should I trust you?
M. T. Ribeiro, S. Singh, and C. Guestrin. "why should I trust you?": Explaining the predictions of any classifier. InProceedings of the 22nd ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, pages 1135–1144, 2016
2016
-
[19]
L. S. Shapley. A value for n-person games.Contributions to the Theory of Games, 2(28):307– 317, 1953
1953
-
[20]
Slack, S
D. Slack, S. Hilgard, E. Jia, S. Singh, and H. Lakkaraju. Fooling lime and shap: Adversarial attacks on post hoc explanation methods. InProceedings of the AAAI/ACM Conference on AI, Ethics, and Society, pages 180–186, 2020
2020
-
[21]
Štrumbelj and I
E. Štrumbelj and I. Kononenko. A general method for visualizing and explaining black-box regression models. InAdaptive and Natural Computing Algorithms: 10th International Con- ference, ICANNGA 2011, Ljubljana, Slovenia, April 14-16, 2011, Proceedings, Part II 10, pages 21–30....
2011
-
[22]
Sundararajan, A
M. Sundararajan, A. Taly, and Q. Yan. Axiomatic attribution for deep networks. InInterna- tional conference on machine learning, pages 3319–3328. PMLR, 2017
2017
-
[23]
Tsanas and M
A. Tsanas and M. Little. Parkinsons Telemonitoring. UCI Machine Learning Repository, 2009. DOI: https://doi.org/10.24432/C5ZS3N
2009 doi
-
[24]
Yeh, C.-Y
C.-K. Yeh, C.-Y . Hsieh, A. Suggala, D. I. Inouye, and P. Ravikumar. On the (in)fidelity and sensitivity of explanations.Advances in Neural Information Processing Systems, 32, 2019. A Appendix A.1 Shift invariance and centered distributions We begin by establishing that a func...
2019
-
[128]
decision surfaces
and learning rates (0.1, 0.01, 0.001) to identify the configuration yielding optimal model per- formance. All neural network models used Adam [10] as an optimizer. 16 −1.0 −0.5 0.0 0.5 1.0 X1 Value 0.4 0.6 0.8 1.0 Average Prediction Partial Dependence Plot for X1 Mean Predicti...
Reviewed August 7, 2026 · model on record in the stance chip above.
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