1. Department of BiostatisticsUniversity of Copenhagen Øster Farimagsgade 5B 1014 Copenhagen K Denmark
2. Department of Applied Mathematics and Computer SciencesGhent University Krijgslaan 281 S9, 9000 Ghent Belgium
3. Departments of Epidemiology and BiostatisticsHarvard School of Public Health 677 Huntington Avenue, Massachusetts 02115 Boston U.S.A.
4. Department of StatisticsHebrew University Mount Scopus Jerusalem 91905 Israel