1. INSISOC, University of Valladolid, Valladolid, Spain
2. Department of Systems and Computer Engineering, Carleton University, Ottawa, Canada
3. Department of Economics and Business Administration, University of Malaga, Malaga, Spain
4. INSISOC, University of Valladolid, Valladolid, Spain; Department of Economics and Business Administration, University of Malaga, Malaga, Spain