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Clément de CHAISEMARTIN (UCSB) – "Difference-in-Differences Estimators of Intertemporal Treatment Effects"
Time: 04:30 pm – 5:45 pm
Date: 7th of January 2021 exceptionally
Clément de CHAISEMARTIN (UCSB) – “Difference-in-Differences Estimators of Intertemporal Treatment Effects”
Abstract: We consider the estimation of the effect of a policy or treatment, using panel data where different groups of units are exposed to the treatment at different times. We focus on parameters aggregating instantaneous and dynamic treatment effects, as a way to evaluate the welfare effects of the policies that occurred over the duration of the panel. We show that under common trends conditions, these parameters can be unbiasedly estimated by weighted sums of differences-in-differences, provided that at least one group is always untreated, and another group is always treated. Our estimators are valid if the treatment effect is heterogeneous, contrary to the commonly-used event-study regression. We also propose estimators of a dynamic linear model, with group-specific but time-invariant effects of the current and lagged treatments, which may be used to evaluate ex-ante the effect of future policies.
Anthony STRITTMATTER (Laboratoire de Microéconométrie-CREST)