1 National Hospital for Neurology and Neurosurgery, London, UK; University College London Institute of Neurology, London, WC1N 3BG, UK; Queen Square Multiple Sclerosis Centre, London, UK. Electronic address: [email protected].
2 National Hospital for Neurology and Neurosurgery, London, UK; University College London Institute of Neurology, London, WC1N 3BG, UK; Queen Square Multiple Sclerosis Centre, London, UK.
3 Queen Square Multiple Sclerosis Centre, London, UK; Medical Statistics Department, London School of Hygiene and Tropical Medicine, London, UK.