1. Women's Health Research Unit; The Blizard Institute; Barts and the London School of Medicine and Dentistry; London UK
2. Balliol College; University of Oxford; Oxford UK
3. Nuffield Department of Primary Care Health Sciences; University of Oxford; Oxford UK
4. Madrid Cochrane Collaboration Centre; Francisco de Vitoria University; Madrid Spain
5. Clinical Biostatistics Unit; Ramon y Cajal Institute of Research (IRYCIS) and CIBER Epidemiology and Public Health (CIBERESP); Madrid Spain