1. Survey Research Center, Institute for Social Research, University of Michigan, PO Box 1248, Ann Arbor, MI 48106, U.S.A., and Joint Program in Survey Methodology, 1218 LeFrak Hall, University of Maryland, College Park, MD 20742, U.S.A.
2. Cathie Marsh Institute for Social Research, University of Manchester, Humanities Bridgeford Street Building, Manchester M13 9PL, U.K., and Institute for Employment Research, Regensburger Str. 104, Nuremberg 90478, Germany.