Introduction to Differences-in-Differences @MarginalRevolutionUniversity
Introduction to Differences-in-Differences  @MarginalRevolutionUniversity
Uploaded August 2021 | Updated September 2026, 1 week ago
MIT's Josh Angrist introduces differences-in-differences with one of the worst economic events in history: the Great Depression.

Economists still argue about the causes of the Great Depression, but most agree that a key piece of the puzzle was an epidemic of bank failures. Over 9,000 banks failed from 1930 to 1933!

Could the Federal Reserve have prevented this catastrophe?

At the time, regional Federal Reserve branches had considerable policy independence. Some branches helped troubled banks with “easy money”. Others did not, following a “tight money” policy.

Metrics wizards Gary Richardson and William Troost used differences-in-differences to analyze a natural experiment in Mississippi, where one half of the state had tight money while the other half had easy. What did they find?

This introduction to differences-in-differences covers the following:
- Bank failures during the Great Depression
- Easy versus tight monetary policies; moral hazard
- Parallel data trends
- Calculating the treatment effect
- Assumptions for a valid differences-in-differences analysis

**INSTRUCTOR RESOURCES**
Troost/Richardson paper: https://www.journals.uchicago.edu/doi/abs/10.1086/649603
Econometrics test bank: mru.io/kt2
High school teacher resources: mru.io/o15
Professor resources: mru.io/t0f
EconInbox: mru.io/sm5

**MORE LEARNING**
Try out our practice questions: mru.io/wfd
See the full course: mru.io/469
Receive updates when we release new videos: mru.io/7g2
More from Marginal Revolution University: mru.io/c30
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Introduction to Differences-in-Differences

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