Warren Stevens is a technical advisor for the PSI Research & Metrics team. After earning a PhD in health economics, Warren taught at both the London School of Tropical Medicine and the London School of Economics for four years before leading the public health research program at the UKMRC Field Station in the Gambia. Warren was in sub-Saharan Africa for seven years and has been involved in health research and evaluation projects in numerous countries across Africa and Asia. He has also acted as an advisor to the World Bank, UNICEF and the World Health Organization. Warren has authored over twenty articles in peer-reviewed journals, has contributed to several textbooks in health policy and evaluation and has spoken at numerous international conferences. His interests lie in the role of markets in improving access to prevention and treatment in resource-poor countries, and the role of health systems in health inequalities.