Optimal Experiments for Partial Causal Effect Identification

2026-05-07

AI Summary

This study addresses the problem of selecting optimal experiments to maximally reduce the uncertainty bounds of a target causal query when causal effects are only partially identifiable and experimental costs are constrained. The authors formulate this as a maximum utility optimization problem, evaluating each experiment by its worst-case reduction in bound width and leveraging the underlying causal graph structure to efficiently prune low-value candidates. They introduce a novel path-interception rule combined with an ID-algorithm-based identifiability check, enabling linear-time identification of zero-utility experiments and drastically reducing the otherwise super-exponential search space. Empirical results demonstrate that their method prunes 50–88% of candidate experiments on average over random graphs and bnlearn benchmark networks without solving polynomial programs, and successfully identifies the optimal intervention strategy for estimating the effect of physical activity on diabetes using NHANES data.

Abstract

Causal queries are often only partially identifiable from observational data, and experiments that could tighten the resulting bounds are typically costly. We study the problem of selecting, prior to observing experimental outcomes, a cost-constrained subset of experiments that maximally tightens bounds on a target query. We formalize this as the max-potency problem, where epistemic potency measures the worst-case reduction in bound width guaranteed by an experiment, and show that this problem is NP-hard via a reduction from 0-1 knapsack. Building on the polynomial-programming framework of Duarte et al. (2023), we give a general procedure for evaluating epistemic potency in discrete settings. To control the super-exponential search space, we introduce two graphical pruning criteria that depend only on the causal graph and the query: a novel path-interception rule that exploits district structure to certify zero potency in linear time, and an identifiability check based on the ID algorithm. On Erdos-Renyi random graphs and 11 bnlearn benchmark networks, the two criteria together prune 50-88% of candidate experiments on average without solving a single polynomial program. For the general subset search, we show that ID-pruned experiments are combinatorially inert, yielding a super-exponential reduction in the number of subsets evaluated. We close with an end-to-end demonstration on observational NHANES data, selecting optimal experiments for estimating the effect of physical activity on diabetes.

Problem

• causal effect identification
• experimental design
• bound tightening
• cost-constrained optimization
• partial identifiability

Innovation

• epistemic potency
• max-potency problem
• causal effect identification
• graphical pruning
• polynomial programming