1. CIMMYT‐Zimbabwe, P.O. Box MP 163, Mount Pleasant, Harare, Zimbabwe;
2. Department of Business and Social Sciences, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada;
3. Savanna Agricultural Research Institute, Tamale, Ghana;
4. Department of Agricultural Economics, Purdue University, 1145 Krannert Building, West Lafayette, IN 47907‐1145, USA