1. Department of Statistics and Actuarial Science, School of Mathematical Sciences, C. K. Tedam University of Technology and Applied Sciences, Kassena-Nankana Navrongo-Kologo Road, Navrongo P.O. Box 24, Upper East, Ghana
2. Department of Mathematics, LMNO, CNRS-Université de Caen, Campus II, Science 3, 14032 Caen, France