1. The Vanguard Group, Inc., PO Box 2600, Valley Forge, PA, 19482-2600 ();
2. Survey Research Center, University of Michigan, Ann Arbor, MI, 48109-1248 ();
3. Department of Economics, Carleton University, Ottawa, ON, K1S 5B6, Canada ();
4. Department of Economics, and Survey Research Center, University of Michigan, Ann Arbor, MI, 48109-1248, and NBER ()