NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH
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Design-based Analysis in Difference-In-Differences Settings with Staggered Adoption

Susan Athey, Guido W. Imbens

NBER Working Paper No. 24963
Issued in August 2018
NBER Program(s):Industrial Organization, Labor Studies

In this paper we study estimation of and inference for average treatment effects in a setting with panel data. We focus on the setting where units, e.g., individuals, firms, or states, adopt the policy or treatment of interest at a particular point in time, and then remain exposed to this treatment at all times afterwards. We take a design perspective where we investigate the properties of estimators and procedures given assumptions on the assignment process. We show that under random assignment of the adoption date the standard Difference-In-Differences estimator is an unbiased estimator of a particular weighted average causal effect. We characterize the properties of this estimand, and show that the standard variance estimator is conservative.

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Document Object Identifier (DOI): 10.3386/w24963

 
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