Matthew Thompson | Oxford Centre for Monitoring and Diagnosis, Department of Primary Care Health Sciences, University of Oxford, UK & Department of Family Medicine, Oregon Health & Science University, Portland, Oregon, USA Ann Van den Bruel | Department of Primary Care Health Sciences, University of Oxford, Oxford, UK Series Editors: Carl Heneghan, Centre for Evidence-Based Medicine, Oxford, UK, Rafael Perera, Department of Primary Care, University of Oxford, UK; Douglas Badenoch, Minervation Ltd, Edinburgh, UK