Michael Anderson is Assistant Professor, Department of Agricultural and Resource Economics, University of California, Berkeley, CA 94720 . Funding from the National Institute on Aging, through grant T32-AG00186 to the National Bureau of Economic Research, is gratefully acknowledged. The author thanks Josh Angrist, David Autor, Jon Gruber, three anonymous referees, and an associate editor for their valuable insights, as well as Larry Schweinhart and Zongping Xiang of High/Scope, Frances Campbell and... (2008-12-01時点)