1. Institute of Public Health; Medical Faculty; University of Heidelberg; Im Neuenheimer Feld 324; 69120 Heidelberg; Germany
2. Hub for Trials Methodology Research; MRC Clinical Trials Unit and University College London; Aviation House, 125; Kingsway; London; WC2B 6NH; UK
3. IMBI; Freiburg University Medical Center; Stefan-Meier-Str.; 26, 79100; Freiburg; Germany