Causal Forests & Generalized Random Forests (GRF, Athey & Wager, Stanford) establishes rigorous non-parametric estimation of Conditional Average Treatment Effects (CATE:
τ(x)=E[Y(1)−Y(0)∣X=x]) with asymptotic Gaussian normality; Unlike standard Random Forests maximizing label purity, Causal Forests introduce: 1) Causal Splitting Rules: maximizing the heterogeneity variance of treatment effects across child nodes
Δτ2 to recursively isolate treatment-sensitive subgroups; 2) Honest Tree Estimation: partitioning training data such that tree structure splits are determined on sample set
Str while leaf treatment effects are evaluated on an independent holdout sample set
Sest, eliminating adaptive overfitting bias; 3) Pointwise Confidence Intervals: providing closed-form asymptotic standard errors for individual causal estimates.