1. Department of Management and Quantitative Methods in Economics, University of Plovdiv Paisii Hilendarski, 4000 Plovdiv, Bulgaria
2. Department of Marketing and International Economic Relations, University of Plovdiv Paisii Hilendarski, 4000 Plovdiv, Bulgaria
3. Department of Economic Sciences, University of Plovdiv Paisii Hilendarski, 4000 Plovdiv, Bulgaria