[1] Ruhr Univ Bochum, Dept Med Informat Stat & Epidemiol, D-4630 Bochum, Germany
[2] Univ Regensburg, Dept Orthoped, Bad Abbach, Germany
[3] Univ Marburg, Inst Med Biometry & Epidemiol, Marburg, Germany
[4] Univ Marburg, Dept Med Physiol, Marburg, Germany
[5] Univ Marburg, Ctr Clin Trials, Marburg, Germany
[6] Univ Marburg, Marburg, Germany
[7] Ruhr Univ Bochum, BG Klin Bergmannsheil, Dept Pain Management, D-4630 Bochum, Germany
[8] Ruhr Univ Bochum, Dept Med Informat Stat & Epidemiol, D-4630 Bochum, Germany
[9] Ctr Clin Acupuncture & Res, Dusseldorf, Germany