1 Institute of Applied Health Research, University of Birmingham, Birmingham, UK. k.hemming@bham.ac.uk.
2 Biostatistics Department, University of Liverpool, Liverpool, UK.
3 Department of Ophthalmology, School of Medicine University of Colorado, Aurora, USA.
4 Applied Health Research Centre (AHRC), Li Ka Shing Knowledge Institute of St. Michael's Hospital, Department of Medicine and Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada.
5 Department of Medicine, Women's College Research Institute, University of Toronto, Toronto, Canada.
6 MRC Clinical Trials Unit at UCL, Institute of Clinical Trials & Methodology, London, UK.