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Working Paper
An Evaluation of Difference-in-Differences Methods Using Placebo Event Studies
Researchers are faced with the choice of which of the many recently developed difference-in-differences methods to use in practice. To assess these estimators' relative performance for single-unit event studies, we conduct 134,000+ state-level placebo event studies across 13 estimators. We find that no single method dominates. Performance is context-dependent, with synthetic-control-like methods sometimes outperforming and sometimes underperforming two-way-fixed-effect-like and matching methods. Performance also varies across states at least as much as it does across estimators. Our results ...