1. Department of Business Studies, School of Economics and Business, University of Salamanca, Campus Miguel de Unamuno, P.° Francisco Tomás y Valiente, s/n, 37007 Salamanca, Spain
2. Escuela Técnica Superior de Ingeniería Industrial, University of Salamanca, Avda. Fernando Ballesteros, 2, 37700 Béjar, Spain
3. Facultad de la Energía, Universidad Nacional de Loja, Avda. Reinaldo Espinoza, Loja 110110, Ecuador