1. Economics Department, Chancellor College, University of Malawi, PO Box 280, Zomba, Malawi
2. Centre for Health Economics, University of York, Heslington, York YO10 5DD, UK
3. Luxembourg Institute of Socio-Economic Research (LISER), Maison des Sciences Humaines, 11, Porte des Sciences, L-4366 Esch-sur-Alzette/Belval