1. Department of Economics, New York University, 19 W. 4th Street, New York, NY 10012, NBER, and Poverty Action Lab (e-mail: )
2. Duke University, 230 Social Sciences Building, Durham, NC 27708, and NBER (e-mail: )
3. Department of Economics, City University of New York, Graduate Center, 365 5th Avenue, Room 5313, New York, NY 10016 (e-mail: )