1. Department of Economics and Econometrics, Pakistan Institute of Development Economics, Islamabad, Pakistan
2. Department of Mathematics, College of Science and Humanities in Al–Kharj, Prince Sattam University, Prince Sattam Bin Abdulaziz University, Al–Kharj 11942, Saudi Arabia
3. Department of Mathematics, College of Science and Arts, Qassim University, Ar Rass, Saudi Arabia
4. Statistics Department, Faculty of Sciences, King AbdulAziz University, Jeddah 21551, Saudi Arabia