针对回归任务设计局部公平性约束,平衡公平与精度。
Fair regression under localized demographic parity constraints
- 在特定分位点/得分阈值上施加群体公平约束,避免全分布约束过严。
- 提出闭式解的公平离散化预测器,网格细化时误差趋近于零。
- 无需模型改动,后处理即可实现公平性修正,适合实际部署。
人口均等性(DP)是一种广泛使用的群体公平准则,要求预测分布对敏感群体保持不变。虽然在分类中自然适用,但在回归任务中全分布的DP常过于严格,导致显著准确率损失。本文提出一种针对回归的DP松弛方法,仅在有限个分位点和/或得分阈值上强制公平性。具体地,引入一种($\ell$, Z)-公平预测器,对每组$S=s$的累积分布函数(CDF)在预设点$(\ell_m, z_m)$处施加约束:$F_{f|S=s}(z_m) = \ell_m$。我们通过拉格朗日对偶形式推导出最优公平离散化预测器的闭式解,并量化了离散化代价,证明风险差距随网格细化而趋于零。进一步设计了一种基于两样本的模型无关后处理算法(有标签样本用于学习基线回归器,无标签样本用于校准),并建立了约束违反与超额惩罚风险的有限样本保证。此外,还引入两种替代框架,分别在选定得分阈值上匹配群体与边际的CDF值,在这两种情况下也给出了最优公平离散化预测器的闭式解。合成与真实数据实验展示了可解释的公平-精度权衡,可在决策相关分位点或阈值处进行针对性修正,同时保持预测性能。
原文摘要 · Abstract (English)
Demographic parity (DP) is a widely used group fairness criterion requiring predictive distributions to be invariant across sensitive groups. While natural in classification, full distributional DP is often overly restrictive in regression and can lead to substantial accuracy loss. We propose a relaxation of DP tailored to regression, enforcing parity only at a finite set of quantile levels and/or score thresholds. Concretely, we introduce a novel (${\ell}$, Z)-fair predictor, which imposes groupwise CDF constraints of the form F f |S=s (z m ) = ${\ell}$ m for prescribed pairs (${\ell}$ m , z m ). For this setting, we derive closed-form characterizations of the optimal fair discretized predictor via a Lagrangian dual formulation and quantify the discretization cost, showing that the risk gap to the continuous optimum vanishes as the grid is refined. We further develop a model-agnostic post-processing algorithm based on two samples (labeled for learning a base regressor and unlabeled for calibration), and establish finite-sample guarantees on constraint violation and excess penalized risk. In addition, we introduce two alternative frameworks where we match group and marginal CDF values at selected score thresholds. In both settings, we provide closed-form solutions for the optimal fair discretized predictor. Experiments on synthetic and real datasets illustrate an interpretable fairness-accuracy trade-off, enabling targeted corrections at decision-relevant quantiles or thresholds while preserving predictive performance.
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