1. University of Oxford; Nuffield Department of Primary Care Health Sciences; Radcliffe Observatory Quarter Woodstock Road Oxford Oxon UK OX2 6GG
2. University of Tasmania; Department of Medicine and Paramedicine, Faculty of Health; Hobart Tasmania Australia
3. University of Washington; Department of Family Medicine; Box 354696 Seattle WA USA 98195-4696
4. University of Oxford; Bodleian Health Care Libraries; Knowledge Centre, ORC Research Building, Old Road Campus Oxford Oxfordshire UK OX3 7DQ