title: Authors' response.
authors.affiliation: Centre for Primary Care and Public Health, Queen Mary University of London. E-mail: j.robson@qmul.ac.uk.
authors.forename: John
authors.initials: J
authors.lastname: Robson
authors.affiliation: Consultant Physician, Barts Health NHS Trust, London.
authors.forename: Tahseen
authors.initials: T
authors.lastname: Chowdhury