用干预后的得分几何分析因果方向,突破传统观测数据的局限。
Interventional Score Geometry for Causal Inference
- 构建干预后得分场,通过变量自由度变化捕捉因果影响
- 相同观测得分下,不同模型干预响应可差异显著
- 为随机试验、工具变量等提供统一几何解释框架
设 $p(x)$ 为变量 $X$ 的联合密度,$ψ(x)=\nabla_x\log p(x)$ 为其得分场。仅基于 $p$ 与 $ψ$ 构建的几何结构无法识别因果方向:具有相同观测分布的结构模型拥有相同的得分几何。本文提出干预的类比形式。硬干预 $\operatorname{do}(X_k=ξ)$ 不仅重加权联合分布,更将其限制在子流形 ${x_k=ξ}$ 上,其得分应定义在剩余 $d-1$ 个自由坐标上。将 $X_k\rightsquigarrow X_j$ 定义为 $X_j$ 的干预边缘分布随 $ξ$ 的变化,并证明该边缘干预得分的导数是因果影响的局部充分条件。对观测得分投影至允许的干预方向通常无法恢复因果响应:两个模型可能共享相同的观测得分和允许集,但响应不同。因此引入由结构信息提供的干预响应场。定义因果度量为具有共同目标的一族干预上的 Fisher 信息度量,避免跨目标的病态比较。该框架为随机试验、工具变量及条件独立设计提供了几何字典,明确各方法能与不能识别的内容。双变量高斯示例显示:两模型具有相同观测得分,但干预得分导数不同。该框架组织了设计、干预与得分场之间的关系,但不超出底层假设带来的识别能力。在 Pearl 的因果之梯中,观测得分几何属于关联层,干预索引得分场属于干预层,个体水平反事实几何留待未来工作。
原文摘要 · Abstract (English)
Let $p(x)$ be the joint density of variables $X$, and let $ψ(x)=\nabla_x\log p(x)$ be its score field. Geometry constructed from $p$ and $ψ$ alone cannot identify causal direction: structural models with the same observational distribution have the same score geometry. I develop an interventional analogue. A hard intervention $\operatorname{do}(X_k=ξ)$ does not merely reweight the joint law; it restricts the distribution to the submanifold ${x_k=ξ}$. Its score should therefore be defined on the remaining $d-1$ free coordinates. I define causal influence $X_k\rightsquigarrow X_j$ as variation of the interventional marginal distribution of $X_j$ with $ξ$, and show that the corresponding derivative of the marginal interventional score gives a local sufficient condition for influence. Projecting the observational score onto admissible intervention directions does not generally recover causal response: two models may share the same observational score and admissible set yet respond differently. I therefore introduce an interventional response field supplied by structural information. A causal metric is defined as the Fisher information metric on a family of interventions with a common target, avoiding ill-posed comparisons across targets. The framework yields a geometric dictionary for randomized trials, instrumental variables, and conditional-independence designs, clarifying what each does and does not identify. A bivariate Gaussian example gives two models with the same observational score but different interventional score derivatives. The framework organizes relations among designs, interventions, and score fields, but adds no identification beyond the underlying assumptions. In Pearl's Ladder of Causation, observational score geometry belongs to association, intervention-indexed score fields to intervention, and unit-level counterfactual geometry is left for future work.
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