1. a I-BioStat , Universiteit Hasselt , Diepenbeek, Belgium
2. b I-BioStat , Katholieke Universiteit Leuven , Leuven, Belgium
3. c School of Statistics , University of Philippines , Diliman, Quezon City, Philippines
4. d Department of Medical Statistics , London School of Hygiene and Tropical Medicine , London, United Kingdom