1. Department of Agricultural and Resource Economics, University of California, 303 Giannini Hall, Berkeley, CA 94720, USA
2. Centre for Energy Studies, Cambridge Institute for Advanced Studies, King Str. 23, Cambridge CB1 1AH, UK
3. Department of Trade and Finance, Faculty of Economics and Management, Czech University of Life Sciences Prague, Kamýcká 129, Prague 6, 165 00 Prague, Czech Republic
4. Department of Quantitative Methods, Faculty of Management, Rzeszow University of Technology, 35-959 Rzeszow, Poland