1. 1 Matej Bel University, Faculty of Economics , Banská Bystrica , Slovakia .
2. 2 Stredoslovenská distribučná, a.s., Žilina , Slovakia .
3. 3 Matej Bel University, Faculty of Economics , Banská Bystrica , Slovakia .
4. 4 University of Bath , Department of Economics , Bath , United Kingdom .