We have benefited from the comments of a number of people. In particul
ar, we thank Rob Alessie, Christopher Carroll, Gary Engelhardt, Willia
m Gale, Luigi Guise, Alan Gustman, Michael Hurd, Arie Kapteyn, Arthur
Kennickell, Laurence Kotlikoff, Robert Miller Jorn-Steffen Pischke, Jo
hn Sabelhaus, Jonathan Skinner, Steven Venti, and three referees for c
omments. We also thank Sanjay Natarajan and Cigdem Ozgokmen for resear
ch assistance. This research was supported in part by a grant from the
Canadian SSHRC.