1. Nuffield Department of Primary Care Health Sciences; University of Oxford; Oxford UK
2. Department of Primary Care Health Sciences; University of Oxford; Oxford UK
3. Iberoamerican Cochrane Centre - Biomedical Research Institute Sant Pau (IIB Sant Pau); CIBER Epidemiología y Salud Pública (CIBERESP); Barcelona Spain
4. Department of Primary Care Clinical Sciences; Clinical Sciences Building, University of Birmingham; Birmingham UK