1. Department of Methodology and Statistics; Maastricht University; Maastricht the Netherlands
2. I-BioStat; Universiteit Hasselt; B-3590 Diepenbeek Belgium
3. I-BioStat; Katholieke Universiteit Leuven; B-3000 Leuven Belgium
4. International Drug Development Institute (IDDI); Louvain-la-Neuve; Belgium