Clément de Chaisemartin
Department of Economics
University of California at Santa Barbara
Santa Barbara, CA 93106
NBER Program Affiliations:
NBER Affiliation: Faculty Research Fellow
Institutional Affiliation: University of California at Santa Barbara
NBER Working Papers and Publications
|September 2019||Estimating the Effect of Treatments Allocated by Randomized Waiting Lists.|
with Luc Behaghel: w26282
Oversubscribed treatments are often allocated using randomized waiting lists. Applicants are ranked randomly, and treatment offers are made following that ranking until all seats are filled. To estimate causal effects, researchers often compare applicants getting and not getting an offer. We show that those two groups are not statistically comparable. Therefore, the estimator arising from that comparison is inconsistent when the number of waitlists goes to infinity. We propose a new estimator, and show that it is consistent, provided the waitlists have at least two seats. Finally, we revisit an application, and we show that using our estimator can lead to significantly different results from those obtained using the commonly used estimator.
|May 2019||Two-way Fixed Effects Estimators with Heterogeneous Treatment Effects|
with Xavier D'Haultfoeuille: w25904
Linear regressions with period and group fixed effects are widely used to estimate treatment effects. We show that they identify weighted sums of the average treatment effects (ATE) in each group and period, with weights that may be negative. Due to the negative weights, the linear regression estimand may for instance be negative while all the ATEs are positive. In two articles that have used those regressions, half of the weights are negative. We propose another estimator that solves this issue. In one of the articles we revisit, it is of a different sign than the linear regression estimator.