[1] Univ Birmingham, Coll Med & Dent Sci, Inst Appl Hlth Res, Birmingham B15 2TT, W Midlands, England
[2] Univ Birmingham, Coll Med & Dent Sci, Primary Care Clin Sci, Birmingham B15 2TT, W Midlands, England
[3] Univ Birmingham, Coll Med & Dent Sci, Med Sociol, Birmingham B15 2TT, W Midlands, England
[4] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Oxford OX1 2JD, England
[5] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Evidence Based Med, Oxford OX1 2JD, England
[6] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Postgrad Studies, Oxford OX1 2JD, England