1. Abdul Latif Jameel Poverty Action Lab, Massachusetts Institute of Technology, 30 Wadsworth Street, Cambridge, MA 02142, USA.
2. Program in Economics, History, and Politics, Harvard University, Cambridge, MA 02138, USA.
3. Department of Economics, University of Zürich, Blümlisalpstrasse 10, Zürich 8006, Switzerland.
4. Department of Psychology and Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544, USA.