Authors: John Macleod; Chris Salisbury; Nicola Low; Anne McCarthy; Jonathan A C Sterne; Aisha Holloway; Rita Patel; Emma Sanford; Andrea Morcom; Paddy Horner; George Davey Smith; Susan Skidmore; Alan Herring; Owen Caul; F D Richard Hobbs; Matthias Egger Journal: BMJ Date: 2005-04-04