Foundations

Build your causal inference intuition from first principles. These 8 chapters follow a running mystery that gradually reveals why causal inference is hard, what tools we have, and how the field learned to do it well.

1. Why Causal Inference?

The fundamental problem of causal inference — why comparing treated and untreated is not enough.

A government launches a job training program. Trainees earn more. Did the program work?

2. The Anatomy of a Research Design

The pipeline from question to credible answer — every step matters.

Now that we know comparison isn't enough, what does a credible research design look like?

3. Selection Bias and Confounding

The single biggest threat to your research — and the reason every method on this site exists.

The people who signed up for training were different. How different? Let's measure it.

4. The Language of Identification

Estimand, estimator, estimate. ATE, ATT, LATE. The precise vocabulary you need.

Now that you feel the problem, let's equip you with the language to talk about it precisely.

5. DAGs for Beginners

A visual tool for thinking about causal relationships — draw the problem, see the solution.

What if we could draw a picture of the training problem and see exactly what's going wrong?

6. A Taxonomy of Identification Strategies

The full toolkit — design-based, model-based, experimental, and quasi-experimental approaches.

Here are all the tools we have to solve problems like the training mystery.

7. Working with Data

Loading, cleaning, reshaping, and constructing variables — the unglamorous but essential work.

Before we can analyze anything, we need to understand what good data looks like.

8. The Credibility Revolution

How empirical economics transformed itself — and what it means for your research.

The mystery resolved: here's how the field actually learned to answer questions like ours.

Start the Research Mystery

A government launches a job training program. Trainees earn more afterward. Did the program actually work? Follow the mystery to find out.

Begin Chapter 1 →