首次实现从可实证的反事实数据中完整识别因果问题，突破非参数因果推断的理论极限。
Causal Identification from Counterfactual Data: Completeness and Bounding Results
- 提出CTFIDU+算法，从任意反事实分布中识别因果查询。
- 证明该算法在反事实识别任务中完全性，揭示可识别性的理论边界。
- 为不可识别的反事实量提供新解析界，实验证明反事实数据能收紧边界。
以往关于反事实识别完备性的研究局限于观测或干预分布（Pearl因果层级的第1、2层），因普遍认为反事实分布（第3层）无法获取。然而，近期工作（Raghavan & Bareinboim, 2025）形式化定义了一类可通过实验方法直接估计的反事实分布，称为反事实可实现性。这开启了新问题：在获得部分第3层数据的前提下，哪些反事实量可被识别？本文提出CTFIDU+算法，用于从任意第3层分布集合中识别反事实查询，并证明其对这一任务具有完备性。基于此，我们确立了从物理可实现分布中可识别反事实的理论极限，从而揭示非参数设定下精确因果推断的根本限制。针对某些关键反事实量不可识别的情况，我们利用可实现的反事实数据导出新型解析界，并通过模拟验证，反事实数据确实在实践中有助于收紧不可识别量的界限。
原文摘要 · Abstract (English)
Previous work establishing completeness results for counterfactual identification has been circumscribed to the setting where the input data belongs to observational or interventional distributions (Layers 1 and 2 of Pearl's Causal Hierarchy), since it was generally presumed impossible to obtain data from counterfactual distributions, which belong to Layer 3. However, recent work (Raghavan & Bareinboim, 2025) has formally characterized a family of counterfactual distributions which can be directly estimated via experimental methods - a notion they call counterfactual realizabilty. This leaves open the question of what additional counterfactual quantities now become identifiable, given this new access to (some) Layer 3 data. To answer this question, we develop the CTFIDU+ algorithm for identifying counterfactual queries from an arbitrary set of Layer 3 distributions, and prove that it is complete for this task. Building on this, we establish the theoretical limit of which counterfactuals can be identified from physically realizable distributions, thus implying the fundamental limit to exact causal inference in the non-parametric setting. Finally, given the impossibility of identifying certain critical types of counterfactuals, we derive novel analytic bounds for such quantities using realizable counterfactual data, and corroborate using simulations that counterfactual data helps tighten the bounds for non-identifiable quantities in practice.
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