Igbozurike, Martin
Scandinavian Institute of African Studies, 1976
Buku Teks
Manchester University Press, 1971
Buku Teks
National Research Institute of Agricultural Economic, Ministry of Agriculture, Forestry and Fisheries , 2000
Buku Teks
Institute of Southeast Asian Studies, 2007
Buku Teks
United Nations Development Programme, 1980
Buku Teks