Synthetic Data That Protects Privacy: A Smarter Approach

Author: Denis Avetisyan


New research demonstrates a more effective neural network technique for generating realistic, privacy-preserving tabular datasets, addressing limitations of existing methods.

MargNet initializes a model with comprehensive marginal distributions, then refines it through adaptive selection and fitting to effectively synthesize data.
MargNet initializes a model with comprehensive marginal distributions, then refines it through adaptive selection and fitting to effectively synthesize data.

MargNet adaptively selects and fits marginal distributions to improve differentially private tabular data synthesis, particularly on complex, highly correlated datasets.

Despite a prevailing consensus favoring statistical models, differentially private tabular data synthesis often struggles with datasets exhibiting dense correlations. This paper, ‘Beyond One-Size-Fits-All: Neural Networks for Differentially Private Tabular Data Synthesis’, challenges this notion by demonstrating the potential of neural networks to capture complex dependencies overlooked by traditional approaches. We introduce MargNet, a novel framework that adaptively selects marginals and trains neural networks to generate high-fidelity synthetic data, achieving significant performance gains-up to 26% reduction in fidelity error-particularly on densely correlated datasets. Could this adaptive approach represent a paradigm shift in balancing privacy and utility for complex tabular data?


The Precarious Balance: Data Sharing and Individual Privacy

The unfettered sharing of raw data, while potentially accelerating scientific discovery and fostering innovation, introduces substantial privacy risks to individuals whose information is contained within those datasets. Each record, even seemingly innocuous details, can contribute to a profile that, when combined with other publicly available information, allows for the identification of individuals – a process known as re-identification. This vulnerability discourages participation in research, particularly in sensitive areas like healthcare and genomics, as individuals reasonably fear the exposure of personal details. Consequently, valuable datasets remain siloed, hindering progress in fields reliant on large-scale data analysis and limiting the potential for breakthroughs that could benefit society. The tension between maximizing data accessibility and safeguarding individual privacy therefore presents a critical challenge for researchers, policymakers, and data scientists alike.

Despite widespread implementation, conventional data anonymization methods – such as suppression, generalization, and pseudonymization – are increasingly vulnerable to re-identification attacks. These attacks leverage the principle of quasi-identification, where seemingly innocuous attributes, when combined, can uniquely pinpoint individuals within a dataset. Studies demonstrate that even datasets stripped of direct identifiers like names and social security numbers can be successfully linked to external records – such as publicly available voter lists or consumer databases – to reveal the identities of individuals. The proliferation of large datasets and advanced data mining techniques has exacerbated this problem, as attackers can exploit subtle correlations and patterns to bypass traditional safeguards. Consequently, reliance on these methods alone is insufficient for ensuring robust privacy protection, prompting the development of more sophisticated techniques like differential privacy and data synthesis.

Achieving robust data synthesis necessitates a delicate equilibrium between safeguarding individual privacy and preserving the usefulness of the generated data for analytical purposes. Simply removing identifying information, while historically common, often proves insufficient against sophisticated re-identification techniques; therefore, advanced synthesis methods focus on creating entirely new datasets that statistically resemble the original without containing actual individual records. This process involves carefully controlling the level of generalization and adding noise to ensure that while overall trends and relationships are maintained – allowing for valid research and model training – the risk of linking synthetic records back to specific individuals is minimized. The efficacy of any synthesis technique is therefore judged not solely on its ability to obscure identities, but on its capacity to retain sufficient data utility, measured by the performance of analytical tasks or machine learning models trained on the synthetic data compared to the original.

Differential Privacy: Laying the Foundation for Secure Synthesis

The Gaussian Mechanism and Exponential Mechanism are core techniques for achieving differential privacy by intentionally perturbing data with noise. The Gaussian Mechanism adds noise drawn from a Gaussian distribution – typically $N(0, \sigma^2)$ – to a numerical query’s output; the scale of the noise, $\sigma$, is calibrated to the query’s sensitivity and the desired privacy parameter $\epsilon$. The Exponential Mechanism, conversely, is used for non-numerical outputs, assigning probabilities to each possible output proportional to $exp(\epsilon \cdot Q(output) / (2 \cdot sensitivity))$, where $Q(output)$ is a utility function and sensitivity measures the maximum change in the utility score caused by a single record’s alteration. Both mechanisms guarantee that the probability of any output remains approximately the same whether or not a single individual’s data is included in the dataset, thus providing differential privacy.

The effectiveness of the Gaussian and Exponential Mechanisms in achieving differential privacy is contingent upon appropriate parameter selection; specifically, the amount of noise added must be calibrated to the sensitivity of the query and the desired privacy level, $\epsilon$. Insufficient noise compromises privacy guarantees, potentially enabling identification of individuals within the dataset. Conversely, excessive noise, while strengthening privacy, degrades the utility of the data, reducing its accuracy and value for analytical purposes. Consequently, practitioners must carefully tune parameters, often employing techniques like cross-validation or utilizing prior knowledge of data distributions, to strike an optimal balance between these competing objectives. The relationship between privacy loss ($\epsilon$), query sensitivity, and noise scale dictates this trade-off, necessitating a nuanced approach to parameter setting.

Statistical methods and Active Inference Modeling (AIM) are established techniques for generating synthetic tabular datasets while preserving differential privacy. Statistical methods typically involve adding noise to aggregate statistics computed from the original data, ensuring that individual records cannot be re-identified from the synthetic data. AIM goes further by learning a probabilistic model of the original data distribution and sampling from this model, subject to privacy constraints enforced via mechanisms like the Gaussian or Exponential Mechanism. Both approaches aim to create datasets that accurately reflect the characteristics of the original data, enabling data analysis and machine learning tasks without compromising individual privacy. The utility of the synthetic data is directly related to the calibration of the noise added or the complexity of the learned model, necessitating a trade-off between privacy and accuracy.

Comparing PGM and NN fitting, iteratively selected marginals demonstrate a decreasing ℓ1 distance error, indicating improved accuracy with each selection.
Comparing PGM and NN fitting, iteratively selected marginals demonstrate a decreasing ℓ1 distance error, indicating improved accuracy with each selection.

Neural Networks: A Path Towards Sophisticated Synthesis

Neural network-based methods have become prominent in data generation due to their ability to model complex data distributions. Generative Adversarial Networks (GANs) utilize a two-network system – a generator and a discriminator – to iteratively learn and produce synthetic data resembling the training dataset. Diffusion Models operate by progressively adding noise to data and then learning to reverse this process, enabling the generation of new samples. Large Language Models (LLMs), initially designed for natural language processing, demonstrate capabilities in generating various data types, including text, code, and even images, by predicting the next element in a sequence. These techniques differ in their architectures and training procedures, but all leverage the learning capacity of neural networks to create synthetic datasets for applications where real data is limited, sensitive, or unavailable.

Differentially private stochastic gradient descent (DP-SGD) and Differentially Private Mixture of Experts with Random Features (DP-MERF) are techniques used to train neural networks while providing formal privacy guarantees. DP-SGD achieves privacy by clipping individual gradients and adding noise proportional to the sensitivity of the computation, scaled by the privacy parameter $\epsilon$ and the batch size. This process ensures that the contribution of any single data point to the learned model is limited. DP-MERF, conversely, employs a mixture of experts model with random feature maps to reduce the dimensionality of the data, followed by applying differential privacy mechanisms. Both methods introduce controlled randomness to obscure individual data records, preventing membership inference attacks and satisfying $\epsilon$-differential privacy, a mathematical standard for data privacy.

PATE-GAN, Generalized Expectation Maximization (GEM), and related techniques utilize neural network architectures to improve synthetic data generation, particularly focusing on privacy preservation. PATE-GAN combines Generative Adversarial Networks (GANs) with differentially private training via the PATE (Private Aggregation of Teacher Ensembles) framework, allowing for the generation of realistic data while limiting the risk of membership inference attacks. GEM, conversely, employs an expectation-maximization approach to learn a generative model without relying on explicit gradients, offering another avenue for privacy-preserving data synthesis. These methods often involve training a teacher network on the sensitive data, then using a student network – a GAN or other generative model – to learn from the teacher’s outputs, effectively obscuring individual data points within the generated synthetic dataset.

On the Adult dataset, MargNet, DP-MERF, and GEM demonstrate improved machine learning efficacy and reduced query/fidelity errors when utilizing resampled inputs compared to fixed inputs.
On the Adult dataset, MargNet, DP-MERF, and GEM demonstrate improved machine learning efficacy and reduced query/fidelity errors when utilizing resampled inputs compared to fixed inputs.

Adaptive Marginal Selection: Refining the Art of Privacy-Preserving Synthesis

During data synthesis, the creation of realistic yet privacy-protected datasets hinges on identifying the most informative features – those that best capture the underlying relationships within the original data. This process, known as marginal selection, is not merely a preliminary step but a crucial determinant of the synthetic data’s utility. By focusing on these key features, synthesis algorithms can efficiently reconstruct the essential characteristics of the original dataset, avoiding the inclusion of redundant or irrelevant information that could compromise privacy without adding value. A robust marginal selection strategy ensures the synthetic data accurately reflects the patterns and correlations present in the original data, maximizing its usefulness for downstream tasks like machine learning model training and statistical analysis. Without careful consideration of feature importance, synthetic datasets risk becoming either overly generic – lacking the nuance needed for meaningful analysis – or inadvertently revealing sensitive information through the preservation of less-critical, yet uniquely identifying, characteristics.

Adaptive Marginal Selection represents a significant advancement in differentially private data synthesis by moving beyond static feature selection. This dynamic approach continuously re-evaluates which features are most informative – and therefore pose the greatest privacy risk – throughout the data generation process. Instead of pre-determining a fixed set of features to protect, the algorithm intelligently adjusts its strategy, prioritizing the preservation of privacy for sensitive attributes while maximizing the utility of the synthesized data. By adaptively balancing these competing concerns, the system can achieve a superior trade-off, releasing data that is both statistically representative of the original dataset and effectively anonymized.

MargNet represents a significant advancement in differentially private data synthesis by seamlessly integrating adaptive marginal selection with the power of neural networks and a dedicated Privacy Filter. This innovative architecture doesn’t just generate synthetic datasets; it carefully prioritizes the most informative features while rigorously enforcing privacy constraints. Evaluations on the Gauss50 dataset demonstrate MargNet’s superior performance, achieving a noteworthy 26% reduction in fidelity error compared to the established Adversarial IMputation method (AIM). This improvement indicates that synthetic data produced by MargNet more closely mirrors the statistical properties of the original data, making it substantially more useful for downstream analysis without compromising individual privacy. The system’s design facilitates a balance between data utility and privacy preservation, offering a robust solution for sensitive data sharing and analysis.

Recent advancements in differentially private data synthesis have yielded MargNet, a system engineered for substantial gains in computational efficiency. The architecture demonstrably outperforms existing methods, specifically the widely-used AIM algorithm, achieving an average speedup of 7x across benchmark datasets. This acceleration stems from a streamlined implementation of adaptive marginal selection and optimized neural network integration, allowing for quicker iterations during the data generation process. Consequently, researchers and practitioners can now synthesize high-fidelity, privacy-preserving datasets in a fraction of the time previously required, facilitating more rapid innovation and broader application of this critical technology.

AIM and MargNet demonstrate comparable ℓ1 distance errors across Adult, Gauss10 (ε=1.0), and Gauss30 (ε=10.0) datasets when fitting marginals, as indicated by the consistent mean error values.
AIM and MargNet demonstrate comparable ℓ1 distance errors across Adult, Gauss10 (ε=1.0), and Gauss30 (ε=10.0) datasets when fitting marginals, as indicated by the consistent mean error values.

The pursuit of generative models, as demonstrated by MargNet, often involves a tension between preserving data utility and ensuring privacy. This work navigates that challenge with an adaptive approach to marginal selection, recognizing the inherent complexity of real-world tabular data. G. H. Hardy observed, “A mathematician, like a painter, is a maker of patterns.” MargNet, in its design, echoes this sentiment – crafting a pattern of synthesized data that faithfully represents the original, but with the essential safeguard of differential privacy. The adaptive algorithm, by focusing on relevant marginals, distills the data to its core elements, embodying a principle of elegant reduction-removing what obscures, to reveal the underlying structure.

What Lies Ahead?

The demonstrated efficacy of MargNet, while notable, does not obviate the inherent tension within differentially private synthesis. The pursuit of utility, predictably, remains tethered to the cost of privacy. Future work must address not merely the degree of this tradeoff, but its very framing. Current metrics, focusing on statistical similarity, offer an incomplete assessment. A dataset perfectly mirroring marginal distributions may still fail to capture critical dependencies, or, conversely, conceal vital anomalies. The field requires a shift toward evaluating synthetic data based on its performance in downstream tasks – a pragmatic, rather than purely probabilistic, validation.

Furthermore, the adaptive marginal selection within MargNet, while effective, introduces a computational complexity that scales with dataset dimensionality. A truly scalable solution necessitates algorithms that approximate this adaptability without sacrificing privacy guarantees. Exploration of techniques such as kernel methods, or even distillation from larger, more complex models, may prove fruitful. Unnecessary complexity, however, remains violence against attention; elegance, even in privacy-preserving mechanisms, is paramount.

Ultimately, the goal is not merely to generate data, but to create a framework for responsible data sharing. This demands a move beyond purely synthetic approaches, toward hybrid models that combine real and synthetic observations under rigorous privacy constraints. The question is not simply ‘how much’ privacy can be sacrificed for utility, but ‘how little’ is necessary. The answer, predictably, will lie not in algorithmic innovation alone, but in a deeper understanding of the information contained within data itself.


Original article: https://arxiv.org/pdf/2511.13893.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/

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2025-11-19 15:04