Affiliations

• ¹ Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK. Electronic address: christopher.butler@phc.ox.ac.uk.
• ² Primary Care Research Centre, University of Southampton.
• ³ Oxford Clinical Trials Research Unit, Botnar Research Centre, University of Oxford, Oxford, UK.
• ⁴ Berry Consultants, Austin, Texas, USA, and Department of Biostatistics, Vanderbilt University School of Medicine, Tennessee, USA.
• ⁵ Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.