1. Department of Community Based Medicine; Academic Unit of Primary Health Care; University of Bristol Cotham House Cotham Hill Bristol UK BS6 6JL
2. Royal College of Surgeons in Ireland Medical School; Department of Family Medicine and General Practice; Mercer's Medical Centre Lower Stephen Street Dublin Ireland 2
3. London School of Hygiene & Tropical Medicine; Department of Epidemiology & Population Health; Keppel Street London UK WC1E 7HT