1. Centre for Evaluation, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK
2. Centre for Sexual Health and HIV AIDS Research (CeSHHAR) Zimbabwe, 9 Monmouth Road, Harare, Zimbabwe
3. RTI International, 351 California Street, Suite 500, San Francisco, CA, USA
4. Institute for Global Health, UCL, Royal Free Hospital, Rowland Hill Street, London, UK and
5. Department of International Public Health, Liverpool School of Tropical Medicine, Pembroke Pl, Liverpool, UK