1. Faculty of Mathematics and Informatics, Konstantin Preslavsky University of Shumen, Shumen, Bulgaria;
2. Department of Statistics, University of Valparaiso, Valparaíso, Chile;
3. Linz Institute of Technology (LIT), Johannes Kepler University in Linz, Linz, Austria;
4. Department of Applied Statistics, Johannes Kepler University in Linz, Linz, Austria