The Causal Layer
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The Causal Layer

Causal inference, econometrics, and the methods behind defensible decisions.

Applied writing on causal inference and econometrics, for analysts and decision-makers who want rigor without the textbook padding.

Marketing Mix Modeling: The Bayesian Way
70 min
marketing analytics
causal inference
bayesian
mmm
R

A practitioner’s walkthrough of Bayesian marketing mix modeling: what an MMM is, why the Bayesian framing is used, the five ways it fails to identify what it claims to…

Nov 2, 2026

The Sharp Edge of the Cutoff: A Practitioner’s Guide to Regression Discontinuity Design
61 min
causal inference
econometrics
RDD
Imagine you manage the analytics function at a large retailer. Your loyalty programme awards “Gold” status (and a 15% discount) to any customer who spends at least £5,000 in…
Oct 25, 2026

Instrumental Variables: Finding Causal Effects with a Lucky Accident
64 min
causal inference
econometrics
instrumental variables
R

When treatment and outcome share an unobserved cause, no amount of covariate adjustment fixes the bias. A practitioner’s guide to instrumental variables: from the Vietnam…

Oct 19, 2026

The Average Treatment Effect Is Often the Wrong Metric
69 min
causal inference
heterogeneous treatment effects
policy learning
experimentation
R

A practitioner’s walkthrough of why the average treatment effect is the default and wrong estimand for most decisions: what the ATE hides, the CATE for heterogeneity, the…

Oct 12, 2026

Long-Term Effects & Universal Holdouts: When Your Lift Disappears
67 min
A/B testing
experimentation
causal inference
product analytics
holdout groups

Short-run A/B tests systematically overstate long-run business impact due to novelty and learning effects. This post explores why your initial lift disappears over time and…

Oct 5, 2026

G-Computation: The Causal Tool You Should Be Using After Regression
34 min
causal inference
g-computation
R
marginaleffects

Why reading regression coefficients directly is rarely sufficient for decision-making, and how g-computation delivers the causal estimates that actually answer business…

Sep 28, 2026
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Applied writing on causal inference and econometrics, for analysts and
decision-makers who want rigor without the textbook padding.

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© 2026 João Vieira

The Causal Layer — Applied writing on causal inference, pricing, and forecasting.