1. Mohamed Ibrahim:
Department of Applied, Mathematical and Actuarial Statistics, Faculty of Commerce, Damietta University,Damietta,Egypt
2. M. Masoom Ali:
Department of Mathematical Sciences Ball State University,Muncie, Indiana 47306,USA
3. Hafida Goual:
Laboratory of Probability and Statistics, University of Badji Mokhtar,Annaba,Algeria
4. Haitham M. Yousof:
Department of Statistics, Mathematics and Insurance, Benha University,,Egypt