1. Department of Biosystems, Division MeBioS, KU Leuven, Kasteelpark Arenberg 30, B-3001 Heverlee, Belgium
2. Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Heverlee, Belgium
3. Leuven Statistics Research Centre, KU Leuven, Celestijnenlaan 200B, B-3001 Heverlee, Belgium