1. Pain Research Unit, Churchill Hospital; Cochrane Pain, Palliative and Supportive Care Group; Churchill Hospital Oxford Oxfordshire UK OX3 7LE
2. Caribbean Institute for Health Research; Chronic Disease Research Centre; The University of the West Indies Jemotts Lane Bridgetown Barbados BB11115
3. Jefferson Medical College, Thomas Jefferson University; Cardeza Foundation for Hematologic Research, Department of Medicine; 1015 Walnut Street Philadelphia USA PA 19107-5099
4. University of Oxford; Pain Research and Nuffield Department of Clinical Neurosciences (Nuffield Division of Anaesthetics); Pain Research Unit Churchill Hospital Oxford Oxfordshire UK OX3 7LE