提出新方法生成更鲁棒、多样且可行动的反事实解释。
Synthesising Counterfactual Explanations via Label-Conditional Gaussian Mixture Variational Autoencoders
- 用标签条件高斯混合变分自编码器学习结构化潜在空间。
- 通过插值生成解释路径,确保对输入和模型扰动鲁棒。
- 支持用户约束,适合需要可解释性与决策建议的场景。
反事实解释(CEs)为算法决策影响的个体提供补救建议。主要挑战在于生成对各类扰动(如输入和模型扰动)均鲁棒的解释,同时满足合理性(位于数据流形上)和多样性(为单一输入提供多个不同补救方案)。现有方法大多无法统一、无模型依赖地解决这些多重需求。本文提出新型生成框架:首先引入标签条件高斯混合变分自编码器(L-GMVAE),在潜在空间中为每类标签学习一组具有多样化原型中心的高斯成分;在此基础上,提出LAPACE(LAtent PAth Counterfactual Explanations)算法,通过从输入潜在表示插值到已学习的潜在原型中心,生成完整的反事实路径。该方法天然具备对输入变化的鲁棒性,因为同一目标类别的所有路径均收敛至固定原型中心。此外,生成路径提供了多种补救选项,使用户可在接近度与合理性之间权衡,同时增强对模型变化的鲁棒性。用户指定的动作可行性约束也可通过轻量级梯度优化在解码器中轻松融入。全面实验表明,LAPACE计算高效,在八项量化指标上表现优异。
原文摘要 · Abstract (English)
Counterfactual explanations (CEs) provide recourse recommendations for individuals affected by algorithmic decisions. A key challenge is generating CEs that are robust against various perturbation types (e.g. input and model perturbations) while simultaneously satisfying other desirable properties. These include plausibility, ensuring CEs reside on the data manifold, and diversity, providing multiple distinct recourse options for single inputs. Existing methods, however, mostly struggle to address these multifaceted requirements in a unified, model-agnostic manner. We address these limitations by proposing a novel generative framework. First, we introduce the Label-conditional Gaussian Mixture Variational Autoencoder (L-GMVAE), a model trained to learn a structured latent space where each class label is represented by a set of Gaussian components with diverse, prototypical centroids. Building on this, we present LAPACE (LAtent PAth Counterfactual Explanations), a model-agnostic algorithm that synthesises entire paths of CE points by interpolating from inputs' latent representations to those learned latent centroids. This approach inherently ensures robustness to input changes, as all paths for a given target class converge to the same fixed centroids. Furthermore, the generated paths provide a spectrum of recourse options, allowing users to navigate the trade-off between proximity and plausibility while also encouraging robustness against model changes. In addition, user-specified actionability constraints can also be easily incorporated via lightweight gradient optimisation through the L-GMVAE's decoder. Comprehensive experiments show that LAPACE is computationally efficient and achieves competitive performance across eight quantitative metrics.
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