Authors: Nadeem Hasan, BM BCh, MA (Cantab), MSc, MFPH, DRCOG, specialty registrar in public health, London, UKCaroline Watson, BM BCh, MA (Oxon), MRCP, specialty registrar in haematology, Oxford, UK Joyee Basu, BM BCh, MA (Oxon), MRCP, specialty registrar in cardiology, Oxford, UK Series Editor: Saran Shantikumar, BA, BSc, MBChB, MRCS, academic clinical fellow in public health, University of Warwick, UK