[1] Univ Freiburg, Clin Trials Unit, Fac Med, Hugstetter Str 55, D-79106 Freiburg, Germany
[2] Univ Freiburg, Med Ctr, Hugstetter Str 55, D-79106 Freiburg, Germany
[3] Inst Qual & Efficiency Hlth Care, Dept Med Biometry, Cologne, Germany
[4] Univ Ulm, Inst Stat, D-89069 Ulm, Germany
[5] Heidelberg Univ, Inst Med Biometry & Informat, Heidelberg, Germany
[6] Univ Freiburg, Inst Med Biometry & Stat, Fac Med, Hugstetter Str 55, D-79106 Freiburg, Germany