# How Much Should We Trust Differences-in-Differences Estimates?

@article{Bertrand2001HowMS, title={How Much Should We Trust Differences-in-Differences Estimates?}, author={Marianne Bertrand and Esther Duflo and Sendhil Mullainathan}, journal={Experimental \& Empirical Studies eJournal}, year={2001} }

Most Difference-in-Difference (DD) papers rely on many years of data and focus on serially correlated outcomes. Yet almost all these papers ignore the bias in the estimated standard errors that serial correlation introduce4s. This is especially troubling because the independent variable of interest in DD estimation (e.g., the passage of law) is itself very serially correlated, which will exacerbate the bias in standard errors. To illustrate the severity of this issue, we randomly generate…

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