[1] Univ Penn, Dept Econ, 133 S 36th St, Philadelphia, PA 19104 USA
[2] Northwestern Univ, Dept Econ, 2211 Campus Dr, Evanston, IL 60208 USA
[3] Univ Amsterdam, Amsterdam Sch Econ, Roetersstr 11, NL-1018 WB Amsterdam, Netherlands
[4] Yale Univ, Dept Econ, New Haven, CT 06520 USA