ECONOMETRICS RESEARCH SEMINAR	INVITATION
R E M I N D E R The Department of Economics and Finance at the Institute for Advanced Studies cordially invites you to the following Econometrics Research Seminar Thursday, October 1, 2015 Attention – New Address Institute for Advanced Studies Josefstädter Strasse 39, 1080 Vienna Lecture Room E02, ground floor 9:00 am (Please note that the seminar will start at 9 am sharp!) Clement de Chaisemartin University of Warwick Fuzzy Differences-in-Differences Abstract: In many applications of the differences-in-differences (DID) method, the treatment increases more in the treatment group, but some units are also treated in the control group. In such fuzzy designs, a popular estimator of treatment effects is the DID of the outcome divided by the DID of the treatment, or OLS and 2SLS regressions with time and group fixed effects estimating weighted averages of this ratio across groups. We start by showing that when the treatment also increases in the control group, this ratio estimates a causal effect only if treatment effects are homogenous in the two groups. Even when the distribution of treatment is stable, it requires that the effect of time be the same on all counterfactual outcomes. As this assumption is not always applicable, we propose two alternative estimators. The first estimator relies on a generalization of common trends assumptions to fuzzy designs, while the second extends the changes-in-changes estimator of Athey & Imbens (2006). When the distribution of treatment changes in the control group, treatment effects are partially identified. Finally, we prove that our estimators are asymptotically normal and use them to revisit applied papers using fuzzy designs. paper jointly with Xavier D'Haultfoeuille We are looking forward to seeing you! Institute for Advanced Studies Department of Economics and Finance Josefstädterstraße 39, 1080 Vienna, Austria Tel.: +43 1 599 91 145 e-Mail: economics@ihs.ac.at http://economics.ihs.ac.at		LINKS DIRECTIONS TO IHS on Google maps ECONOMICS SEMINARS IN VIENNA on Google calendar IHS Department of Economics and Finance Dept of Economics and Finance @IHS_Eco_Fin Institute for Advanced Studies @IHS_Vienna
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