[1] Univ Med Ctr Utrecht, Julius Ctr Hlth Sci & Primary Care, Utrecht, Netherlands
[2] MRC, Biostat Unit, Cambridge CB2 2BW, England
[3] Radboud Univ Nijmegen, Dept Epidemiol Biostat & HTA, Med Ctr, NL-6525 ED Nijmegen, Netherlands
[4] London Sch Hyg & Trop Med, Dept Med Stat, London WC1, England
[5] Univ Oxford, Ctr Stat Med, Oxford, England