Causal Inference

Dependencies

This skill requires the bayesian-workflow skill for all PyMC modeling steps (priors, sampling, diagnostics, calibration, reporting).

Detect it:

ls ~/.claude/skills/bayesian-workflow/SKILL.md 2>/dev/null || ls .claude/skills/bayesian-workflow/SKILL.md 2>/dev/null

If not found, install it:

git clone https://github.com/Learning-Bayesian-Statistics/baygent-skills.git /tmp/baygent-skills
cp -r /tmp/baygent-skills/bayesian-workflow ~/.claude/skills/

For all PyMC modeling steps (priors, sampling, diagnostics, calibration, reporting), follow the bayesian-workflow skill.

Workflow overview

Every causal analysis follows this sequence. Steps 1-4 are the thinking phase (no code). Steps 5-8 are the doing phase. Think before you do.

1. Formulate the causal question — Propose precise estimand (ATE, ATT, LATE, etc.). ⚠️ ASK USER TO CONFIRM.
2. Draw the DAG — Propose causal graph with nodes, edges, and explicit non-edges. ⚠️ ASK USER TO CONFIRM. See references/dags-and-identification.md
3. Identify — Determine identification strategy (backdoor, front-door, IV, RDD, DiD). ⚠️ ASK USER TO CONFIRM untestable assumptions. See references/dags-and-identification.md
4. Choose design — Match problem to method using table below. ⚠️ ASK USER TO CONFIRM. See references/quasi-experiments.md or references/structural-models.md
5. Estimate — Build and fit the model. Delegate all PyMC mechanics to bayesian-workflow skill.
6. Refute — MANDATORY. Run design-specific robustness checks. See references/refutation.md
7. Interpret — Effect size + decision-relevant HDIs + probability of direction.
8. Report — Generate <treatment>-on-<outcome>/report.md using the canonical template in references/reporting.md. Run scripts/check_refutation.py to turn refutation outcomes into pass/marginal/fail ratings, calibrated causal language (causal / suggestive / associational / descriptive), and an ordered next-steps list. Use that output to fill the report's section 7 (causal language calibration) and Suggested Next Steps.

Design selection guide

Before reading the table, walk the intake — it routes you to a design and surfaces the assumptions you'll have to defend later:

1. Restate the estimand. ATE, ATT, LATE, or a CATE? On whom, over what period? If you can't write the one-sentence estimand, you don't have a causal question yet — you have a dataset.
2. Identify the data shape. Single time series, wide panel of units, long unit–time panel, cross-section, or pre/post group data?
3. Identify the treatment assignment. Known intervention time, staggered adoption, a threshold/cutoff, a kink, an instrument, or observed treatment with confounders?
4. State the identifying story. What makes the comparison causal — parallel trends, no anticipation, no manipulation at the cutoff, a valid instrument, overlap/positivity, donor support? This is exactly what you'll refute later.
5. Recommend one primary design + alternatives — and reconcile with the estimand. Name the best-fit design from the table plus any plausible cross-check. Then check that the estimand from step 1 is the one the design actually identifies: DiD → ATT (on the treated); RDD → a local effect at the cutoff; IV → LATE for compliers (under monotonicity); SC → the treated-unit effect. If they differ, change the design or re-scope the estimand and say so. If two designs agree later, that's convergent evidence rather than reliance on a single identification.

Critical rules

• No estimation without a confirmed DAG. A causal graph is not optional decoration — it makes assumptions explicit and determines the adjustment set. If the user resists, explain why the DAG is non-negotiable before proceeding.
• The DAG licenses adjustment, not timing — pre-treatment is necessary, not sufficient. Pre-treatment timing only rules out two post-treatment hazards: collider bias (conditioning on a common effect of treatment and outcome) and over-control (conditioning on a mediator). It does not by itself make a variable safe to adjust for. A pre-treatment variable can still be a collider on a back-door path — M-bias: a common effect of an unobserved cause of treatment and an unobserved cause of the outcome — and adjusting for it induces confounding that wasn't there. So include a covariate only if (a) it is pre-treatment and (b) the DAG shows it blocks a back-door path and is not itself a collider (or a descendant of one) on an otherwise-blocked path — i.e. it satisfies the back-door/adjustment criterion. Timing is the quick screen; the graph is the authority. (Deliberate mediation analysis is the principled exception to the post-treatment ban: it conditions on a post-treatment mediator on purpose to estimate a different estimand — direct vs. indirect effects — under stronger assumptions, including no treatment-induced mediator–outcome confounding; declare it as mediation, don't slip it in as confounder control.) If the covariates that actually satisfy the back-door criterion are too thin to identify the effect, say so and frame the result as descriptive, not causal.
• No causal claims without refutation. Every design has failure modes. Run at minimum one design-specific robustness check (placebo test, sensitivity analysis, falsification test) before reporting results. See references/refutation.md.
• State assumptions before results. Lead with what must be true for the estimate to be causal. Bury the estimate after the assumptions, not before. This is not optional politeness — it prevents misuse of results.
• Adapt HDIs to the decision context. The bayesian-workflow skill's 94% HDI is a sensible default; adapt it with explicit explanation when the decision stakes warrant it (e.g., 89% for exploratory, 97% for high-stakes policy). Report multiple intervals when the decision threshold matters.
• Downgrade causal language when warranted. If identification assumptions are unverifiable or refutation raises flags, soften claims: "consistent with a causal effect" not "causes", "estimated effect" not "true effect". Flag uncertainty loudly in the report.
• Use scripts/check_refutation.py to calibrate language, not human judgment. The script takes a structured refutation.json (see its docstring for schema) and returns a calibrated level — causal / suggestive / associational / descriptive — plus an ordered list of next steps. Use the script's output verbatim in the report; expand only with problem-specific context. Hand-rolled language calibration is exactly where overclaiming creeps in.
• Always generate <treatment>-on-<outcome>/report.md after the analysis. Store all artifacts (inference_data.nc, dag.png, effect_posterior.png, forest.png, design-specific figures, refutation.json, effect_summary.csv) in the slug-named results folder, and produce report.md from the canonical template in references/reporting.md. The report is the audit trail; code without an interpreted, fixed-shape report is incomplete.
• Ask the user when domain knowledge is needed. You cannot know whether an instrument is valid, whether parallel trends holds, or whether a confounder exists without domain expertise. Ask before assuming.
• Delegate PyMC mechanics to bayesian-workflow. This skill handles causal structure and design. The bayesian-workflow skill handles priors, sampling, diagnostics, calibration, and reporting format. Don't duplicate those rules here.

Common gotchas

These are battle-tested lessons that save hours of debugging:

• CausalPy formula syntax uses C() for categoricals. Passing a string column directly without C() will silently produce wrong dummy coding. Always wrap categorical treatment and group variables: "y ~ C(treatment) + C(group)".
• DoWhy requires explicit U nodes for unobserved confounders. Omitting them from the graph will make DoWhy treat your model as fully identified when it isn't. Add latent nodes explicitly and mark them as unobserved.
• CausalPy's PyMC models don't auto-store log-likelihood. Same issue as bayesian-workflow: nutpie silently drops it. Call pm.compute_log_likelihood(idata, model=model) after sampling if you need it for model comparison.
• Parallel trends is untestable in the post-treatment period. Pre-treatment trend tests are necessary but not sufficient — passing them doesn't prove the assumption holds after treatment. State this explicitly in every DiD report.
• Synthetic control requires the treated unit to lie within the convex hull of donors. If the treated unit is an outlier (highest GDP, largest city), no weighted combination of donors can approximate its counterfactual. Check this before running — if violated, the design is invalid.
• DiD group variable must be dummy-coded (0/1). CausalPy rejects string labels like "treatment"/"control". Use integers: 1 = treatment, 0 = control. Data also requires a unit column.
• SyntheticControl expects wide-format data. Index = time, columns = unit names, values = outcome. If your data is long format, pivot first: df.pivot(index="date", columns="unit", values="outcome").

Utility scripts

# Interpret refutation outcomes and calibrate causal language
python scripts/check_refutation.py --refutation <slug>/refutation.json --output <slug>/check_report.json

The refutation.json is written by the analyst from DoWhy/CausalPy refutation outputs. See the script docstring for the JSON schema, the test categories (critical vs. marginal), and the language calibration rules.

When things go wrong