1. Department of Psychosomatic Medicine and Psychotherapy, Medical University Hospital Tuebingen, Tuebingen, Germany
2. Department of Psychosomatic Medicine and Psychotherapy, LVR-Hospital Essen, University of Duisburg-Essen, Essen, Germany
3. Institute for Clinical Epidemiology and Applied Biometry, University Hospital Tuebingen, University of Tuebingen, Tuebingen, Germany
4. Wiegmann Klinik, Hospital for Psychosomatic Medicine and Psychotherapy, DRK Clinic Center Berlin, Berlin, Germany