[1] Wellesley Coll, Fed Reserve Bank Chicago, Chicago, IL USA
[2] NBER, Chicago, IL USA
[3] Smith Coll, Dept Econ, Northampton, MA 01063 USA
[4] NBER, Northampton, MA USA
[5] Williams Coll, Dept Econ, Williamstown, MA USA
[6] NBER, Williamstown, MA USA
[7] Williams Coll, Brookings Inst, Dept Econ, Washington, DC USA
[8] NBER, Washington, DC USA