1. MRC Epidemiology UnitUniversity of Cambridge Cambridge UK
2. School of Health and Related Research, Faculty of Medicine, Dentistry and HealthUniversity of Sheffield Sheffield UK
3. Primary Care Unit, Institute of Public HealthUniversity of Cambridge Cambridge UK
4. Division of Psychological and Social Medicine, School of MedicineUniversity of Leeds Leeds UK
5. Fakenham Medical Practice Norfolk UK
6. Norwich Medical SchoolUniversity of East Anglia Norwich UK