1. Department of Statistics, College of Science, Engineering and Technology, University of South Africa, Pretoria, South Africa
2. Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Hatfield, South Africa
3. Université de Nantes & LS2N UMR CNRS 6004, Nantes, France
4. Department of Mathematical Statistics and Actuarial Science, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, South Africa