1. University Medical Library, University of Basel Basel Switzerland
2. Institute for Research in Operative Medicine, Faculty of Health, School of Medicine Witten/Herdecke University Cologne Germany
3. Wilhelmina Children's Hospital University Medical Center Utrecht Utrecht the Netherlands
4. Department of Internal Medicine IV Medical University of Heidelberg Heidelberg Germany
5. Basel Institute for Clinical Epidemiology and Biostatistics, Department of Clinical Research University Hospital Basel and University of Basel Basel Switzerland