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NBER Working Papers · November 2, 2026 · On the brief until November 16, 2026

How Different are Different Differences-in-Differences? A Large-Scale Meta-Analysis -- by Peter Hull

EconomicsData Science
THE AI ANGLE
Assisting large-scale replication of econometric specifications

A researcher used AI assistance to replicate 1,346 specifications from 108 economics papers to test two-way fixed effects against modern difference-in-differences methods. Traditional estimates correlated strongly with newer techniques and rarely produced statistically significant opposite signs. The findings suggest that negative weighting issues in fixed effects models may present fewer problems in practice than expected.

Summary written by AI Business Lens with an AI model from the article at nber.org. It is not the article, and the publisher has not reviewed it. For publishers.

THE TEACHING ANGLE
Instructors can discuss whether researchers should adopt modern estimators when traditional two-way fixed effects methods provide higher precision and yield similar empirical results.

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