1. Department of Statistics and O.R., Complutense University of Madrid, Plaza de Ciencias 3, Madrid 28040, Spain
2. Institute of Interdisciplinary Mathematics, Complutense University of Madrid, Plaza de Ciencias 3, Madrid 28040, Spain
3. Department of Quantitative Methods for Economics and Business, University of Granada, Paseo de Cartuja 7, Granada 18011, Spain