[1] UCL, Dept Primary Care & Populat Hlth, London, England
[2] Univ Bath, Dept Psychol, Bath, Avon, England
[3] London Sch Hyg & Trop Med, Fac Epidemiol & Populat Hlth, London, England
[4] UCL, Ctr Outcomes Res & Effectiveness, London, England
[5] Univ Oxford, Nuffield Dept Primary Hlth Care Sci, Oxford, England