REVIEW 3 major objections 5 minor 1 cited by
TarDiff: Target-Oriented Diffusion Guidance for Synthetic Electronic Health Record Time Series Generation
T0 review · 3 major / 5 minor · reviewed 2026-08-16 · deepseek-v4-flash
Pith's one-line read Synthetic EHR time series generated by influence-guided diffusion are claimed to improve downstream clinical classifiers beyond distribution-matching baselines.
desk verdict A genuinely new idea—influence-guided diffusion for EHR time series—with consistent reported gains, but the implemented guidance term doesn't match the derived influence and the empirical reporting needs error bars and a cleaner validation story. 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 central object is the influence-gradient term $J = \nabla_{x_t}(G\cdot\nabla_\phi \ell(x_t,y;\phi^*))$, inserted into the reverse diffusion mean as $\tilde{\mu}_t = \mu_t + w J$. Here $G$ is a single cached vector, the normalized sum of downstream-loss gradients over the guidance set, and $\ell$ is the task loss. The design mirrors classifier guidance but replaces the class log-likelihood gradient with a task-utility signal; because $G$ is independent of $x_t$, the per-step guidance reduces to a dot product plus one gradient computation, which is why sampling remains cheap. The intended effect is to push the denoising trajectory toward regions where a synthetic sample's loss gradient aligns with the guidance-set gradient, i.e., toward samples whose addition to the training set would reduce expected task loss.
What would settle it
Compute the true influence of a batch of TarDiff-generated samples by adding each sample to the training set, retraining the downstream classifier, and measuring the loss change on a fixed held-out guidance set; then rank-correlate those true changes with the paper's predicted $\Delta L_T(\hat{z})$ from Eq. (23). If the correlation is not clearly positive on MIMIC-III mortality, the guidance direction is not optimizing the stated objective.
Extended reading notes
Core claim
TarDiff's central claim is that the reverse diffusion update can be modified to $\tilde{\mu}_\theta(x_t,y,t) = \mu_\theta(x_t,y,t) + \alpha \nabla_{x_t}\Delta L_T(\hat{z}_t)$, where $\Delta L_T(\hat{z})$ is the expected reduction in downstream task loss caused by adding synthetic sample $\hat{z}=(x,y)$ to the training set. The paper approximates this influence as $\Delta L_T(\hat{z}) = \nabla_\phi \ell(\hat{z};\phi^*)\cdot G$, with $G$ the accumulated (negative) gradient of the downstream loss over a guidance set drawn i.i.d. from the task distribution. In the implemented pipeline, $G$ is cached once from a pretrained downstream model, and at each denoising step the mean update is $\tilde{\mu}_t = \mu_t + w J$, where $J = \nabla_{x_t}(G\cdot\nabla_\phi \ell(x_t,y;\phi^*))$. The paper reports that this produces synthetic time series that, in TSTR mode, beat a real-data-trained classifier on MIMIC-III mortality (AUPRC 0.1799 vs 0.1736) and outperform five generative baselines across six datasets by up to 20.4% AUPRC and 18.4% AUROC, with one-time gradient-caching overhead of 10-167 seconds.
Load-bearing premise
The load-bearing assumption is that the simplified guidance signal actually points toward synthetic samples that improve the downstream model: the exact influence formula in Eq. (21) has a sample-dependent denominator $\|\nabla_\phi \ell(\hat{z};\phi)\|^2$ that Algorithm 1 omits as a constant factor, and the paper provides no experiment verifying that the simplified direction correlates with true leave-one-out retraining effects.
Editorial extensions
If this is right
- Synthetic-only training with TarDiff can outperform a classifier trained on real data in at least one TSTR setting: MIMIC-III mortality AUPRC 0.1799 vs 0.1736.
- Augmenting real data with TarDiff samples improves downstream AUROC across most tasks and mix ratios, with the gains generally growing as the synthetic proportion rises from 0.2 to 1.0.
- Influence guidance naturally shifts generation toward minority-class patterns; TarDiff raises minority F1 from 0.056 to 0.108 on MIMIC-III and from 0.013 to 0.018 on eICU without explicit class weighting.
- Restricting the guidance set to minority-only samples further raises minority F1 (0.163 on MIMIC-III), while majority-only guidance degrades it (0.066), showing that the guidance direction is controllable.
- The added cost is modest: one-time downstream training plus gradient caching (10-167 s across datasets) and a per-step overhead ratio $g(L,D)/h(L,D)$ that is small, making the task-oriented guidance practical.
Reading between the lines
- My inference: if the reported gains are real, the same cached-gradient guidance could be ported to non-temporal tabular and image data with a well-defined downstream loss, since nothing in the update rule is specific to time series.
- My inference: the minority-only guidance results suggest an explicit, tunable selection rule for the guidance set (for instance, choosing the hardest minority examples), which the paper stops short of specifying.
- My inference: the paper's evidence implies that distributional fidelity alone is an insufficient benchmark for synthetic EHR generation; a utility-first evaluation protocol would report downstream AUPRC/AUROC gains after augmentation, not just distance-to-real-data scores.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes TarDiff, a diffusion-based generative framework for synthetic electronic health record (EHR) time series that aims to generate samples optimized for a downstream clinical task rather than merely for distributional fidelity. The central idea is to use influence functions: the influence of a candidate synthetic sample is defined as the expected reduction in task loss on a guidance set if that sample were added to the training set, and this influence is computed via the gradient inner product between the candidate sample and the cached gradients of the guidance set. This influence gradient is then added to the reverse diffusion mean at each denoising step. The method is evaluated on six datasets (MIMIC-III, eICU, APAVA, ADFD, PTB, TDBrain) in train-on-synthetic/test-on-real (TSTR) and train-on-synthetic-and-real/test-on-real (TSRTR) protocols, reporting AUPRC/AUROC improvements over several GAN, VAE, and diffusion baselines, plus additional analyses on class imbalance, computational overhead, fidelity, and privacy.
Significance. If the central mechanism is valid, the paper makes a valuable contribution: it explicitly targets synthetic data generation toward downstream task utility, which is a recognized weakness of fidelity-only generative models, and it demonstrates consistent gains across multiple clinical datasets and tasks. The paper also provides a useful experimental breadth, including minority-class analysis, guidance-set scale sensitivity, runtime overhead, and privacy metrics. However, the significance is contingent on resolving the mismatch between the influence derivation and the implemented guidance signal, and on providing statistically grounded comparisons; as presented, the evidence does not yet establish that the reported gains arise from the claimed influence objective.
major comments (3)
- [Section 3.3 and Algorithm 1] The implemented guidance signal is not the gradient of the influence function defined in Eq. (21). In Eq. (21), the per-sample denominator ||∇φℓ(ˆz;φ)||^2 depends on the candidate sample ˆz, so it cannot be absorbed into a constant vector G as written in Eq. (22). Algorithm 1 precomputes G from Dguide alone (only accumulating per-sample gradients, then normalizing by |D0|) and then uses J = ∇_{x_t}(G·∇φℓ(x_t,y;φ*)) in Eq. (17). Dropping the denominator changes the guidance direction, because the true gradient of Eq. (21) would include a term from differentiating ||∇φℓ(ˆz;φ)||^2 with respect to x_t. Since Eq. (17) is the core contribution, this mismatch must be fixed or explicitly justified (e.g., by showing the simplified direction is a valid approximation of the true influence gradient).
- [Section 4.6 and evaluation protocol] The guidance scale w is selected on the Evaluation-Val subset, and then the final performance is reported on the entire validation set, which includes Evaluation-Val. This constitutes a form of validation-set overfitting: the reported figures in Figure 3 and the downstream tables may be optimistically biased because the same data used to choose w are retained in the final evaluation. The paper claims this is 'unbiased,' but the overlap between model selection and evaluation invalidates that claim. The final evaluation should be performed on a held-out test set (or at least on a split disjoint from both Guidance-Val and Evaluation-Val).
- [Tables 1, 2, 4, 5 and Figure 2] No error bars, confidence intervals, or seeds are reported for any of the main quantitative results. Several claimed improvements are small (e.g., MIMIC-III mortality AUPRC 0.1799 vs. Real Data 0.1736; PTB AUPRC 0.95435 vs. TimeVAE 0.95092), and without variance estimates it is not possible to assess whether these differences are meaningful. The paper should report mean and standard deviation over at least three independent runs for the primary comparisons.
minor comments (5)
- [Section 2.2] The symbol T is used both for the length of the time series and the number of diffusion steps in Section 2.1; this dual use is confusing and should be disambiguated (e.g., L for series length).
- [Section 3.3] The symbol ε in Eqs. (18)-(22) is used as a small perturbation magnitude but is never defined; it should be clarified whether it is a fixed scalar, a learning rate, or an infinitesimal, since the magnitude of G in Eq. (22) depends on it.
- [Section 4.6 / Figure 3 caption] The text says the right panel reports AUROC on the Evaluation-Val subset, but the Figure 3 caption says 'assessing AUROC performance on the Guidance-Val subset.' These are inconsistent and should be reconciled.
- [Appendix A.3, Table 7] Table 7 lists MIMIC-III as having 26,150 samples, while Section 4.1 and Table 6 report 20,920; one of these is a typo and should be corrected.
- [Appendix A.4] The text refers to a 'PTBrain dataset,' which appears to be a typo for TDBrain.
Circularity Check
Minor self-referential influence check and validation-split tuning; central test-set claims are externally validated and not circular.
-
self definitional
[Section 3.2 Eq. (17), Section 3.3 Eqs. (21)-(23), Algorithm 1, Section 4.6 Figure 3]
"Notice that we can denote the gradient accumulation of the guidance set Dguide by G, we can end up with the following equation: ... ΔLT (ẑ) = ∇ϕℓ(ẑ;ϕ)·G ... (b) J←∇ xt [G·∇ϕℓ(xt,yt;ϕ∗)] ... The left panel illustrates sample influence value changes"
The 'sample influence' plotted in Fig. 3 is the same inner product ∇ℓ(ẑ)·G that Algorithm 1 uses as the guidance objective J, with G cached from Dguide. Increasing the guidance scale w therefore mechanically increases the displayed influence score; the manipulation check is self-referential and cannot validate that the score tracks true leave-one-out loss reduction. In addition, the denominator ||∇ϕℓ(ẑ)||^2 in Eq. (21) depends on the candidate ẑ, so precomputing G without it (Algorithm 1) makes the implemented direction differ from the claimed gradient of ΔLT; this is a correctness flaw rather than a circular prediction, but it reinforces that the 'influence' being optimized is the paper's own definition rather than an externally verified quantity.
full rationale
The paper's headline results (TSTR and TSRTR, Tables 1-5) are evaluated on held-out test sets that are not used to compute the guidance vector G; the guidance set is the validation split, and the downstream TimesNet classifiers are tested on real test data. The reported gains over baselines are therefore empirical and not forced by construction, so the central claim is not circular. However, two mild self-referential elements exist. First, Section 4.6/Figure 3 validates the influence mechanism by plotting the same G·∇ℓ score that is used as the guidance signal, so the observed 'influence increases' are partly by construction rather than an independent check against retraining effects. Second, the paper states that 'throughout all experiments' the standard validation split is the guidance set, and Section 4.6 tunes the guidance scale on a subset of that validation split before reporting final validation performance; this is a mild selection-on-validation issue, though the test-set comparisons are unaffected. There is no load-bearing self-citation chain: the influence-function approximation is attributed to Charpiat et al. and Anand et al., not to the authors' own prior work, and the cited prior papers are not used to forbid alternatives. Overall circularity is low because the principal empirical claims rest on external test-set benchmarks.
Assumptions & free parameters
free parameters (1)
- Influence guidance scale w =
Section 4.6 reports optimal around +1000 for MIMIC/eICU; Appendix D says 100 used in the main experiments
assumptions (4)
- domain assumption The parameter-update rule δφ = ε∇φf(x)/||∇φf(x)||^2 from Charpiat et al. (2019) extends correctly to a loss function ℓ when measuring influence on other samples.
- domain assumption The guidance set D_guide is i.i.d. from the same distribution P as the test data.
- ad hoc to paper Adding the influence gradient to the reverse diffusion mean (Eq. 17) preserves the conditional data distribution well enough to generate samples from the target distribution.
- standard math The first-order Taylor expansion in Eq. (20), ignoring O(||δφ||^2), is accurate for the guidance set.
Cite this review
Pith. "Pith review of TarDiff: Target-Oriented Diffusion Guidance for Synthetic Electronic Health Record Time Series Generation." pith.science (2026). https://pith.science/paper/RJXDRPTE
@misc{pith2026250417613,
author = {Pith},
title = {Pith review of: TarDiff: Target-Oriented Diffusion Guidance for Synthetic Electronic Health Record Time Series Generation},
year = {2026},
howpublished = {\url{https://pith.science/paper/RJXDRPTE}},
note = {Machine review of arXiv:2504.17613}
}
read the original abstract
Synthetic Electronic Health Record (EHR) time-series generation is crucial for advancing clinical machine learning models, as it helps address data scarcity by providing more training data. However, most existing approaches focus primarily on replicating statistical distributions and temporal dependencies of real-world data. We argue that fidelity to observed data alone does not guarantee better model performance, as common patterns may dominate, limiting the representation of rare but important conditions. This highlights the need for generate synthetic samples to improve performance of specific clinical models to fulfill their target outcomes. To address this, we propose TarDiff, a novel target-oriented diffusion framework that integrates task-specific influence guidance into the synthetic data generation process. Unlike conventional approaches that mimic training data distributions, TarDiff optimizes synthetic samples by quantifying their expected contribution to improving downstream model performance through influence functions. Specifically, we measure the reduction in task-specific loss induced by synthetic samples and embed this influence gradient into the reverse diffusion process, thereby steering the generation towards utility-optimized data. Evaluated on six publicly available EHR datasets, TarDiff achieves state-of-the-art performance, outperforming existing methods by up to 20.4% in AUPRC and 18.4% in AUROC. Our results demonstrate that TarDiff not only preserves temporal fidelity but also enhances downstream model performance, offering a robust solution to data scarcity and class imbalance in healthcare analytics.
Figures
Figures from the paper (9 more)
Forward citations
Cited by 1 Pith paper
-
Diff-MN: Diffusion Parameterized MoE-NCDE for Continuous Time Series Generation with Irregular Observations
Diff-MN generates continuous, arbitrary-resolution time series from irregular observations by diffusing MoE-NCDE dynamics weights, reporting consistent wins over KO-VAE and GT-GAN on ten datasets.
Reference graph
Works this paper leans on
-
[1]
Influence scores at scale for efficient language data sampling
Nikhil Anand, Joshua Tan, and Maria Minakova. Influence scores at scale for efficient language data sampling. arXiv preprint arXiv:2311.16298,
-
[8]
TimeDP: Learning to Generate Multi-Domain Time Series with Domain Prompts
Yu-Hao Huang, Chang Xu, Yueying Wu, Wu-Jun Li, and Jiang Bian. Timedp: Learning to generate multi-domain time series with domain prompts. arXiv preprint arXiv:2501.05403,
-
[9]
Timehr: Image-based time series generation for electronic health records
Hojjat Karami, Mary-Anne Hartley, David Atienza, and Anisoara Ionescu. Timehr: Image-based time series generation for electronic health records. CoRR, abs/2402.06318,
-
[10]
Auto-encoding variational bayes
Diederik P Kingma. Auto-encoding variational bayes. arXiv preprint arXiv:1312.6114,
-
[13]
Hao Li, Yu-Hao Huang, Chang Xu, Viktor Schlegel, Ren-He Jiang, Riza Batista-Navarro, Goran Nenadic, and Jiang Bian. Bridge: Bootstrapping text to control time-series generation via multi- agent iterative optimization and diffusion modelling. arXiv preprint arXiv:2503.02445,
-
[15]
Llms are not zero-shot reasoners for biomedical information extraction
Aishik Nagar, Viktor Schlegel, Thanh-Tung Nguyen, Hao Li, Yuping Wu, Kuluhan Binici, and Stefan Winkler. Llms are not zero-shot reasoners for biomedical information extraction. CoRR, abs/2408.12249,
-
[17]
Julian Schön, Raghavendra Selvan, Lotte Nygård, Ivan Richter V ogelius, and Jens Petersen. Explicit temporal embedding in deep generative latent models for longitudinal medical image synthesis. CoRR, abs/2301.05465,
-
[18]
Score-based generative modeling through stochastic differential equations
Yang Song, Jascha Sohl-Dickstein, Diederik P Kingma, Abhishek Kumar, Stefano Ermon, and Ben Poole. Score-based generative modeling through stochastic differential equations. arXiv preprint arXiv:2011.13456,
arXiv 2011
Show all 24 references
-
[19]
Medformer: A multi-granularity patching transformer for medical time-series classification
Yihe Wang, Nan Huang, Taida Li, Yujun Yan, and Xiang Zhang. Medformer: A multi-granularity patching transformer for medical time-series classification. arXiv preprint arXiv:2405.19363,
-
[20]
Time series data augmentation for deep learning: A survey
Qingsong Wen, Liang Sun, Fan Yang, Xiaomin Song, Jingkun Gao, Xue Wang, and Huan Xu. Time series data augmentation for deep learning: A survey. arXiv preprint arXiv:2002.12478,
2002 arXiv
-
[21]
Timesnet: Temporal 2d-variation modeling for general time series analysis
Haixu Wu, Tengge Hu, Yong Liu, Hang Zhou, Jianmin Wang, and Mingsheng Long. Timesnet: Temporal 2d-variation modeling for general time series analysis. arXiv preprint arXiv:2210.02186,
-
[23]
For our analysis, we focus on the first 24 hours of hospitalization for each patient, resulting in 20,920 samples
A Dataset Details A.1 Critical Care EHR Datasets (MIMIC-III and eICU) MIMIC-III[Johnson et al., 2016] is a large, publicly available database comprising de-identified health-related data associated with over 40,000 patients who stayed in critical care units of the Beth Israel ...
2016
-
[1977]
Timevae: A variational auto- encoder for multivariate time series generation
Abhyuday Desai, Cynthia Freeman, Zuhui Wang, and Ian Beaver. Timevae: A variational auto- encoder for multivariate time series generation. arXiv preprint arXiv:2111.08095,
-
[2015]
Data are sampled every 5 minutes, resulting in 288 time steps
For our analysis, we extract time-series measurements (heart rate, respiratory rate, and oxygen saturation) from the initial 24-hour window of ICU admission. Data are sampled every 5 minutes, resulting in 288 time steps. Each time step includes 3 features, providing a granular...
2024
-
[2016]
Transitioning from real to synthetic data: Quantify- ing the bias in model
Aman Gupta, Deepak Bhatt, and Anubha Pandey. Transitioning from real to synthetic data: Quantify- ing the bias in model. arXiv preprint arXiv:2105.04144,
-
[2017]
Vector quantized time series generation with a bidirectional prior model
Daesoo Lee, Sara Malacarne, and Erlend Aune. Vector quantized time series generation with a bidirectional prior model. arXiv preprint arXiv:2303.04743,
-
[2018]
PULSAR at mediqa-sum 2023: Large language models augmented by synthetic dialogue convert patient dialogues to medical records
Viktor Schlegel, Hao Li, Yuping Wu, Anand Subramanian, Thanh-Tung Nguyen, Abhinav Ramesh Kashyap, Daniel Beck, Xiao-Jun Zeng, Riza Theresa Batista-Navarro, Stefan Winkler, and Goran Nenadic. PULSAR at mediqa-sum 2023: Large language models augmented by synthetic dialogue conve...
2023
-
[2019]
Diffusion-ts: Interpretable diffusion for general time series generation
Xinyu Yuan and Yan Qiao. Diffusion-ts: Interpretable diffusion for general time series generation. arXiv preprint arXiv:2403.01742,
-
[2020]
Invdiff: Invariant guidance for bias mitigation in diffusion models
Min Hou, Yueying Wu, Chang Xu, Yu-Hao Huang, Chenxi Bai, Le Wu, and Jiang Bian. Invdiff: Invariant guidance for bias mitigation in diffusion models. CoRR, abs/2412.08480,
-
[2021]
Classifier-free diffusion guidance
Jonathan Ho and Tim Salimans. Classifier-free diffusion guidance. arXiv preprint arXiv:2207.12598,
-
[2022]
Malin, Jon Duke, Walter F
Edward Choi, Siddharth Biswal, Bradley A. Malin, Jon Duke, Walter F. Stewart, and Jimeng Sun. Generating multi-label discrete electronic health records using generative adversarial networks. CoRR, abs/1703.06490,
-
[2023]
Team: PULSAR at probsum 2023: PULSAR: pre-training with extracted healthcare terms for summarising patients’ problems and data augmentation with black-box large language models
Hao Li, Yuping Wu, Viktor Schlegel, Riza Batista-Navarro, Thanh-Tung Nguyen, Abhinav Ramesh Kashyap, Xiao-Jun Zeng, Daniel Beck, Stefan Winkler, and Goran Nenadic. Team: PULSAR at probsum 2023: PULSAR: pre-training with extracted healthcare terms for summarising patients’ prob...
2023
-
[2024]
Controllable financial market generation with diffusion guided meta agent
Yu-Hao Huang, Chang Xu, Yang Liu, Weiqing Liu, Wu-Jun Li, and Jiang Bian. Controllable financial market generation with diffusion guided meta agent. arXiv preprint arXiv:2408.12991,
-
[2025]
Biodiffusion: A versatile diffusion model for biomedical signal synthesis
Xiaomin Li, Mykhailo Sakevych, Gentry Atkinson, and Vangelis Metsis. Biodiffusion: A versatile diffusion model for biomedical signal synthesis. CoRR, abs/2401.10282, 2024a. Yizhi Li, Ge Zhang, Xingwei Qu, Jiali Li, Zhaoqun Li, Noah Wang, Hao Li, Ruibin Yuan, Yinghao Ma, Kai Zh...
Reviewed August 16, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.