[1] Univ Cambridge, Sch Clin Med, Behav Sci, Behav Sci Grp, Cambridge CB2 1TN, England
[2] Univ Cambridge, Sch Clin Med, Primary Care Unit, Inst Publ Hlth, Cambridge CB2 1TN, England
[3] Univ Cambridge, Strangeways Res Lab, Primary Care Res, Primary Care Unit, Cambridge CB2 1TN, England