1. Biostatistical Centre, Katholieke Universiteit Leuven, Kapucijnenvoer 35, B‐3000 Leuven, Belgium
2. Biostatistics, Center for Statistics, Limburgs Universitair Centrum, Universitaire Campus, B‐3590 Diepenbeek, Belgium
3. Institute of Mathematics and Statistics, The University of Kent, Canterbury, Kent CT2 7NF, U.K.