Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, Germany. frank.kramer@med.uni-goettingen.de|Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, Germany. frank.kramer@med.uni-goettingen.de|Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, Germany. frank.kramer@med.uni-goettingen.de|Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, Germany. frank.kramer@med.uni-goettingen.de|Department of Medical Statistics, University Medical Center Göttingen, Humboldtallee 32, Germany. frank.kramer@med.uni-goettingen.de