1. Harvard University, 79 JFK Street, Cambridge, MA 02138 and National Bureau of Economic Reseearch (NBER) and Abdul Latif Jameel Poverty Action Lab (J-PAL) (e-mail: )
2. Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, Building E17, Room 201B, Cambridge, MA 02139 and NBER and J-PAL (e-mail: )
3. University of Chicago, 1126 E. 59th Street, Chicago, IL 60637 and NBER and J-PAL (e-mail: )