1. Mitsui Professor of Economics, Massachusetts Institute of Technology, Cambridge, Massachusetts; President, National Bureau of Economic Research, Cambridge, Massachusetts.
2. DeWalt Ankeny Professor of Economic Policy, Dartmouth College, Hanover, New Hampshire; Research Associate, National Bureau of Economic Research, Cambridge, Massachusetts.
3. John F. Stambaugh Professor of Political Economy, Kennedy School of Government, Harvard University, Cambridge, Massachusetts; Area Director for Health and Retirement Programs and Program Director for Aging, National Bureau of Economic Research, Cambridge, Massachusetts.