Seminar for Applied Stochastics, Department of Statistics, University of Munich, Akademiestrasse 1, D-80799 Munich, Germany. boulesteix@stat.uni-muenchen.de|Seminar for Applied Stochastics, Department of Statistics, University of Munich, Akademiestrasse 1, D-80799 Munich, Germany. boulesteix@stat.uni-muenchen.de|Seminar for Applied Stochastics, Department of Statistics, University of Munich, Akademiestrasse 1, D-80799 Munich, Germany. boulesteix@stat.uni-muenchen.de