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Method library WORKFLOW / 011
Research workflow/6 steps

Evaluating a causal forest fit

Source grf — Athey, Tibshirani & Wager
01
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Method mapInput → 6 steps → output
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ARRIVE ATResults
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Inside the methodReasoning, equations & implementation
Step 1 of 6
01
Estimation

[GRF] Causal forest

The core estimate — where the causal quantity itself is computed.

What happens here

Fit with OOB predictions and variance.

Formula
\tau(x)=\mathbb{E}\!\left[\,Y(1)-Y(0)\mid X=x\,\right]
The estimator

Causal forest — Honest random forest for heterogeneous treatment effects — CATE for a binary treatment via GRF moment conditions.

Reads fromNot specified Feeds into#2#3#4#5
Key code
cf <- causal_forest(X, Y, W)          # Y.hat, W.hat cross-fit
tau.hat <- predict(cf)$predictions    # OOB CATEs
Discussion on this step (0)
StatsOtterDiscussion starter · Editorial note

Before using this step, make its assumptions and its output explicit. A useful peer note explains what you would check, what could go wrong, or what would change your interpretation.

Questions to explore
  1. Which assumption matters most here, and what evidence could challenge it?
  2. What would you check before passing this output to the next step?

Peer discussion

  • Bring your experience, a question, or a different perspective.
02
Data contract

Inputs & data

A fitted causal forest (n=2000, p=10) you want to validate before trusting.

Show data format & exampleHide example

Format — one row per unit. A covariate matrix X (numeric), a binary treatment W ∈ {0,1}, and an outcome Y.

  X1     X2    X3    W    Y
 0.42  -1.1   0     1   3.10
-0.07   0.6   1     0   1.85
 1.20   0.3   0     1   4.02
03
Read the evidence

Results & interpretation

3 figures Workflow discussion 0
01FigureEstimated propensity scores by arm — a quick check on overlap / positivity.
02FigureCovariate balance before vs after IPW weighting.
03FigureDistribution of the per-unit bias diagnostics from test calibration.

Figures reproduced from grf — Athey, Tibshirani & Wager — unofficial community showcase; all credit to the original authors.

Context & interpretation

The GRF 'Evaluating a causal forest fit' tutorial. Before reading anything off a fitted forest, check that it's well-calibrated and that the heterogeneity isn't an artifact of noise. Then look at what's driving the splits and how the CATE relates to interpretable covariates. Unofficial summary.

Peer notes

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IN THE MARGINS

Peer discussion