1. Biostatistical Center, Catholic University of Leuven, U.Z. St.-Rafaèl, Leuven, Belgium,
2. Biostatistical Center, Catholic University of Leuven, U.Z. St.-Rafaèl, Leuven, Belgium
3. Biostatistical Center, Catholic University of Leuven, U.Z. St.-Rafaël, Leuven, Belgium
4. Department of Biostatistics and Medical Informatics, University of Wisconsin, Clinical Science Center, Madison, Wisconsin, USA