Published on in Vol 12 , No 2 (2010) :Apr-Jun
1 Centre for Reviews and Dissemination , University of York , York , GB
2 Public and Environmental Health Research Unit , London School of Hygiene and Tropical Medicine , London , GB
3 School of Social Policy , Sociology and Social Research , , University of Kent , Canterbury , GB
4 MRC General Practice Research Framework , University College London , London , GB
*all authors contributed equally