Editorial Board within it 'DONALD J. HUGHES H. BURR STEINBACH tracts a 1 KONRAD B. KRAUSKOPP WILLIAM L. STRAUS, JR. try. Besic EDWIN M. LERNER EDWARD L. TATUM a strong Editorial Staff SARAH S. DEES, LUCILLE GUINARD, NANCY S. tion to it HAMILTON, WILLIAM HASKELL, OLIVER W. HEATtration s] WOLE, YUKIE KOZAI, JUDITH B. LEVIN, ELLEN with its s E. MURPHY, BETHSABE PEDERSEN, MADELINE SCHNEIDER. NANCY ...

This research was supported by grants from the National Science Foundation and the National Institute on Aging. I am particularly grateful to Ian Domowitz, who provided many important and insightful comments on an earlier draft. Many others provided useful comments: James Coleman, Robert Mare, Lars Muus, Larry Radbill, Nancy Tuma, and an anonymous reviewer. Jean Mitchell and Nancy Winship helpe...