1 Clarendon-Reuben doctoral scholar, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford; PhD student, Bangor University, Bangor.
2 Nuffield Department of Primary Health Care Sciences, University of Oxford, Oxford.
3 Department of Clinical Neurophysiology, Betsi Cadwaldr University Health Board, Bangor, Gwynedd.
4 Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford.