Alasdair Breckenridge1, Colin Dollery2, Michael Rawlins3, Mark Walport4. 1. Medicines and Healthcare products Regulatory Agency, London SW8 5NQ, UK. Electronic address: alasdair.breckenridge@mhra.gsi.gov.uk. 2. GlaxoSmithKline Research and Development, Harlow, Essex, UK. 3. National Institute for Health and Clinical Excellence, London, UK. 4. Wellcome Trust, London, UK.