1. Department of Agricultural and Resource Economics; University of California; Davis, One Shield Avenue; Davis; CA; 95616; USA
2. Department of Applied Economics; University of Minnesota; 1994 Buford Avenue; St. Paul; MN; 55108; USA
3. Center of Research in the Economics of Development; University of Namur; 8 Rempart de la Vierge; B-5000; Namur; Belgium