1. Department of Statistics, Faculty of Sciences, King Abdulaziz Univ., Jeddah 21551, SA, (Corresponding author), e-mail: aslam_ravian@hotmail.com
2. Department of Statistics, National College of Business Administration & Economics, Lahore 54000, PK, e-mail: nas_shan1@hotmail.com
3. Department of Statistics, Forman Christian College Univ., Lahore 54000, PK, e-mail: mazam72@yahoo.com