1. Department of Statistics and Operational Research and Didactics of Mathematics, University of Oviedo, Oviedo, Spain
2. Department of Applied Mathematics, Materials Science and Engineering and Electronic Technology, Rey Juan Carlos University, Madrid, Spain
3. Department of Statistics, Institute of Fundamental Physics and Mathematics, University of Salamanca, Salamanca, Spain
4. Department of Statistics, Faculty of Medicine, University of Salamanca, Salamanca, Spain