1. Nuffield Department of Primary Care Health Sciences, Radcliffe Observatory Quarter, University of Oxford, Woodstock Road, Oxford OX2 6GG, UK
2. St Edmund Hall, University of Oxford, Oxford OX1 4AR, UK
3. Medical Sciences Division, St Peters College, University of Oxford, Oxford OX1 2DL, UK
4. Bodleian Health Care Libraries, Oxford OX3 7DQ, UK