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  5. Pre-event Trends in the Panel Event-Study Design

American Economic Review

ISSN 0002-8282 (Print) | ISSN 1944-7981 (Online)

Pre-event Trends in the Panel Event-Study Design

  • Simon Freyaldenhoven
  • Christian Hansen
  • Jesse M. Shapiro
American Economic Review
vol. 109, no. 9, September 2019
(pp. 3307–38)
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Abstract

We consider a linear panel event-study design in which unobserved confounds may be related both to the outcome and to the policy variable of interest. We provide sufficient conditions to identify the causal effect of the policy by exploiting covariates related to the policy only through the confounds. Our model implies a set of moment equations that are linear in parameters. The effect of the policy can be estimated by 2SLS, and causal inference is valid even when endogeneity leads to pre-event trends ("pre-trends") in the outcome. Alternative approaches perform poorly in our simulations.

Citation

Freyaldenhoven, Simon, Christian Hansen, and Jesse M. Shapiro. 2019. "Pre-event Trends in the Panel Event-Study Design." American Economic Review 109 (9): 3307–38. DOI: 10.1257/aer.20180609

Additional Materials

JEL Classification

  • C23 Single Equation Models; Single Variables: Panel Data Models; Spatio-temporal Models
  • C26 Single Equation Models: Single Variables: Instrumental Variables (IV) Estimation