1. University of Applied Sciences Zwickau, Faculty of Business and Economics, Kornmarkt 1, 08056 Zwickau, Germany (stefan.kolev@fh-zwickau.de)
2. University of Siegen, Faculty of Economics, Business Informatics and Business Law, Unteres Schloss 3, 57072 Siegen, Germany (ekkehard.koehler@uni-siegen.de)