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Disparate Impact in Synthetic Data Generation

Paul Andrey, Michaël Perrot, Batiste Le Bars, Marc Tommasi

cs.LG
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#3771 of 5669 · cs.LG
Tournament Score
1360±50
10501750
53%
Win Rate
9
Wins
8
Losses
17
Matches
Rating
5.5/ 10
Significance6
Rigor5.5
Novelty6
Clarity7

Abstract

We revisit the fairness notion of disparate impact for synthetic data generation (SDG), that assesses whether the utility of generated records is the same across sensitive groups. Our approach departs from existing work on fair SDG, that address the problem of correcting for undue biases in the observed distribution, hence redefining SDG as learning a distribution that is not that of the real data. By contrast, non-disparate impact is notably achieved when the synthetic and real distributions are the same. We expose reasons why SDG may fail to reach that solution and discuss why approximation and estimation errors occur and can be disparate across groups. We notably look into the expressive power of SDG methods relative to distribution complexity, sampling errors due to group proportions, and estimation errors induced by differential privacy mechanisms. We illustrate cases of disparate impact on both artificial and real-world data, focusing on SDG methods that rely on probabilistic graphical models. We also introduce a strategy of learning group-wise SDG models and illustrate how it can improve both the overall utility and its parity in many settings.

AI Impact Assessments

(1 models)

Scientific Impact Assessment: "Disparate Impact in Synthetic Data Generation"

1. Core Contribution

This paper reframes fairness in synthetic data generation (SDG) away from the dominant "de-biasing" paradigm toward a disparate impact assessment: does the SDG method produce synthetic data of equal utility across sensitive groups? The key insight is that even when the goal is to faithfully reproduce the real data distribution (not correct for bias), SDG methods can introduce *new* disparities through unequal approximation and estimation errors across groups. The authors formalize this as Definition 1, identify three structural sources of disparate impact (approximation errors from limited model expressiveness, estimation errors from unbalanced group sizes, and DP-induced noise), and propose a group-wise SDG meta-algorithm as a mitigation strategy.

This conceptual reframing is the paper's strongest intellectual contribution. While prior work (Ganev et al., 2022; Bullwinkel et al., 2022) touched on DP's disparate effects on synthetic data, this paper provides a more comprehensive analysis that separates DP from non-DP sources of disparity and examines their interactions.

2. Methodological Rigor

The experimental methodology is generally sound but has notable limitations:

Strengths:

  • The use of controlled artificial distributions with known graphical structures is well-designed for isolating causal mechanisms. The four settings (base, fewer-samples, higher-complexity, double-disadvantage) systematically vary the hypothesized sources of disparity.
  • Multiple replicas (10 base distributions for artificial data, 10 random splits for ACS) with reported variability provide reasonable robustness.
  • Full reproducibility is claimed with code, data, and seeds made available.
  • The DP proof for the group-wise algorithm (Theorem 1) relies on standard composition results and appears correct.
  • Weaknesses:

  • The paper focuses exclusively on PGM-based SDG methods. While this is justified by the interpretability of hypothesis classes, it limits generalizability. No experiments with GANs, VAEs, or diffusion-based generators are included, leaving open whether the identified mechanisms transfer.
  • The artificial distributions involve only 6 binary attributes — extremely low-dimensional. The gap between these toy settings and real-world complexity is large, and the paper doesn't bridge it convincingly.
  • The ACS experiments use only one dataset with a specific demographic structure. The sensitivity group definition (4 groups with ~10:1 ratio for ethnicity) is somewhat narrow.
  • Statistical significance is not formally tested. Standard deviations are mentioned as "low magnitude" but not reported in main tables, making it difficult to assess whether observed disparities are statistically meaningful.
  • The group-wise modeling approach, while intuitive, is presented without theoretical analysis of when it should help or hurt. The empirical results are indeed mixed — for some methods, group-wise modeling *increases* disparate impact on downstream classifiers, which somewhat undermines the contribution.
  • 3. Potential Impact

    The paper addresses a genuinely important gap: synthetic data is increasingly used as a privacy-preserving data sharing mechanism, and if it systematically degrades representation of minority groups, it could propagate or amplify harm. This is practically relevant for healthcare, census data, and social science applications.

    However, the impact is tempered by:

  • The lack of a strong mitigation strategy. The group-wise approach is a natural baseline but has clear limitations (reduced statistical power, worse DP performance for small groups).
  • The analysis remains largely descriptive rather than prescriptive. The paper identifies *that* disparate impact occurs and *why*, but provides limited guidance on *how to fix it* beyond the group-wise heuristic.
  • The restriction to tabular categorical data with PGM-based methods limits immediate applicability to the broader SDG ecosystem.
  • 4. Timeliness & Relevance

    The paper is timely. Synthetic data is being adopted in regulated domains (healthcare, finance, government statistics) where both privacy and fairness are legal requirements. The EU AI Act and similar regulations make this intersection increasingly relevant. The observation that DP mechanisms can compound existing disparities is important for practitioners implementing privacy-preserving data pipelines.

    The paper also addresses a genuine blind spot in the SDG evaluation literature, which typically reports population-level utility metrics without disaggregation by sensitive groups.

    5. Strengths & Limitations

    Key Strengths:

  • Clean conceptual contribution: separating "fair SDG as de-biasing" from "fair SDG as non-disparate utility" is valuable and well-articulated.
  • Systematic decomposition of error sources (approximation, estimation, DP-induced) with controlled experiments to validate each.
  • The observation that approximation and estimation errors are cumulative (double-disadvantage setting) is insightful.
  • Transparent about limitations of the group-wise approach.
  • Key Limitations:

  • Limited scope of SDG methods studied (PGM only).
  • The formal definition (Definition 1) requires choosing f, u, and τ, making it a framework rather than a concrete criterion. No guidance on selecting τ.
  • Group-wise modeling requires knowing and using sensitive attributes, which may conflict with legal restrictions on processing protected characteristics in some jurisdictions.
  • The paper does not address continuous data, high-dimensional settings, or intersectionality beyond simple group products.
  • Missing comparison with any fair SDG baseline from the de-biasing literature, which would contextualize the relative merits of the two paradigms.
  • Theoretical analysis is informal — the paper identifies mechanisms but provides no formal bounds on disparate impact as a function of group size ratios, distribution complexity, or DP parameters.
  • Overall Assessment

    This is a well-motivated paper that identifies and systematically investigates an underexplored problem. The conceptual contribution of framing SDG fairness as disparate impact is clean and useful. The experimental methodology is careful within its scope but limited in breadth. The paper is more diagnostic than prescriptive — it excels at identifying problems but offers only a preliminary mitigation strategy with mixed results. It represents a solid contribution to the fairness-privacy intersection but falls short of the depth (theoretical bounds) or breadth (diverse SDG methods, datasets) needed for high impact.

    Rating:5.5/ 10
    Significance 6Rigor 5.5Novelty 6Clarity 7

    Generated Jun 12, 2026

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