Yves Patrice ETOGO NYAGA University of Ngaoundéré-Cameroon, Faculty of Economics and Management   FSEG, Université de Ngaoundéré Ngaoundéré, Adamaoua BP 454 Cameroun   etogo_nyaga@yahoo.fr             JEL Areas: O3 : Technological Change; Research and Development: General Q5 : Environmental Economics: General