Affiliation: | Graduate School of Education &Graduate Group in Biostatistics, University of California, Berkeley, California 94720, U.S.A. &Institute of Education, University of London, London WC1H OAL, U.K.;Department of Statistics &Methodology Institute, London School of Economics, London, WC2A 2AE, U.K. &Division of Epidemiology, Norwegian Institute of Public Health, 0403 Oslo, Norway;Division of Epidemiology, Norwegian Institute of Public Health, 0403 Oslo, Norway &Section of Epidemiology and Medical Statistics, University of Bergen, 5020 Bergen, Norway |