1. Harvard Kennedy School, Harvard University, 79 JFK Street, Cambridge, MA 02138 and the NBER.
2. MIT Department of Economics, 50 Memorial Drive, Building E52, Room 355, Cambridge, MA 02142–1347, the NBER and a Board Member of the Commonwealth Connector.
3. Department of Economics, Wellesley College, 106 Central Street, Wellesley, MA 02481 and the NBER.