1. Clinical and Molecular Epidemiology Unit and Clinical Trials and Evidence-Based Medicine Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Greece
2. MRC Biostatistics Unit, Cambridge, UK
3. MRC Health Services Collaboration, Bristol, UK
4. Clinical and Molecular Epidemiology Unit and Clinical Trials and Evidence-Based Medicine Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Greece, , Department of Medicine, Tufts University School of Medicine, Boston, MA, USA