Authors: John D Mathews; Anna V Forsythe; Zoe Brady; Martin W Butler; Stacy K Goergen; Graham B Byrnes; Graham G Giles; Anthony B Wallace; Philip R Anderson; Tenniel A Guiver; Paul McGale; Timothy M Cain; James G Dowty; Adrian C Bickerstaffe; Sarah C Darby Journal: BMJ Date: 2013-05-21