1 MRC Clinical Trials Unit at UCL, University College London, London WC1V 6LJ, UK. Electronic address: a.judd@ucl.ac.uk.
2 MRC Clinical Trials Unit at UCL, University College London, London WC1V 6LJ, UK.
3 MRC Clinical Trials Unit at UCL, University College London, London WC1V 6LJ, UK; Institute for Global Health, University College London, London WC1V 6LJ, UK.