Harvesting Differences-in-Differences and Event-Study Evidence

Alberto Abadie; Joshua Angrist; Brigham Frandsen; Jörn-Steffen Pischke

doi:10.3386/w34550

Harvesting Differences-in-Differences and Event-Study Evidence

Alberto Abadie, Joshua Angrist, Brigham Frandsen & Jörn-Steffen Pischke

Working Paper 34550

DOI 10.3386/w34550

Issue Date December 2025

This paper surveys econometric innovations related to differences-in-differences estimators and event-study models with time-varying treatment effects. Our discussion highlights tricky normalization issues, heterogeneous policy effects, the interpretation of exposure designs, pretrends pretesting, and the ever-bothersome question of logs versus levels. Key ideas are illustrated with applications.

This is a pre-publication draft chapter from "‘Metrics Remastered: An Empiricist's Almanac," Princeton University Press, 2026. We thank Kirill Borusyak for help with code, Nathan Nunn for help with data, and Ahmet Gulek, Merilin Martinson, Samuel McIntyre, and Grace Wang for exemplary research assistance. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.

Joshua Angrist
The work discussed here was funded in part by the Laura and John Arnold Foundation, the National Science Foundation, and the W.T. Grant Foundation.

Joshua Angrist's daughter teaches at a Boston charter school.
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Alberto Abadie, Joshua Angrist, Brigham Frandsen, and Jörn-Steffen Pischke, "Harvesting Differences-in-Differences and Event-Study Evidence," NBER Working Paper 34550 (2025), https://doi.org/10.3386/w34550.

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