Has airline efficiency affected by the inclusion of aviation into European Union Emission Trading Scheme? Evidences from 22 airlines during 2008–2012
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DOI: 10.1016/j.energy.2015.12.039
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- Greer, Mark, 2009. "Is it the labor unions' fault? Dissecting the causes of the impaired technical efficiencies of the legacy carriers in the United States," Transportation Research Part A: Policy and Practice, Elsevier, vol. 43(9-10), pages 779-789, November.
- Ehrlich, Isaac & Georges Gallais-Hamonno & Zhiqiang Liu & Randall Lutter, 1994. "Productivity Growth and Firm Ownership: An Analytical and Empirical Investigation," Journal of Political Economy, University of Chicago Press, vol. 102(5), pages 1006-1038, October.
- Tone, Kaoru & Tsutsui, Miki, 2009. "Network DEA: A slacks-based measure approach," European Journal of Operational Research, Elsevier, vol. 197(1), pages 243-252, August.
- Inglada, Vicente & Rey, Belen & Rodriguez-Alvarez, Ana & Coto-Millan, Pablo, 2006. "Liberalisation and efficiency in international air transport," Transportation Research Part A: Policy and Practice, Elsevier, vol. 40(2), pages 95-105, February.
- Anger, Annela, 2010. "Including aviation in the European emissions trading scheme: Impacts on the industry, CO2 emissions and macroeconomic activity in the EU," Journal of Air Transport Management, Elsevier, vol. 16(2), pages 100-105.
- Charnes, A. & Cooper, W. W. & Rhodes, E., 1978. "Measuring the efficiency of decision making units," European Journal of Operational Research, Elsevier, vol. 2(6), pages 429-444, November.
- Tim Coelli & Sergio Perelman & Elliot Romano, 1999. "Accounting for Environmental Influences in Stochastic Frontier Models: With Application to International Airlines," Journal of Productivity Analysis, Springer, vol. 11(3), pages 251-273, June.
- Baltagi, Badi H & Griffin, James M & Rich, Daniel P, 1995. "Airline Deregulation: The Cost Pieces of the Puzzle," International Economic Review, Department of Economics, University of Pennsylvania and Osaka University Institute of Social and Economic Research Association, vol. 36(1), pages 245-260, February.
- Yang, Hongliang & Pollitt, Michael, 2010. "The necessity of distinguishing weak and strong disposability among undesirable outputs in DEA: Environmental performance of Chinese coal-fired power plants," Energy Policy, Elsevier, vol. 38(8), pages 4440-4444, August.
- Sickles, Robin C. & Good, David & Johnson, Richard L., 1986. "Allocative distortions and the regulatory transition of the U.S. airline industry," Journal of Econometrics, Elsevier, vol. 33(1-2), pages 143-163.
- Cui, Qiang & Kuang, Hai-bo & Wu, Chun-you & Li, Ye, 2013. "Dynamic formation mechanism of airport competitiveness: The case of China," Transportation Research Part A: Policy and Practice, Elsevier, vol. 47(C), pages 10-18.
- Oum, Tae Hoon & Yu, Chunyan, 1998. "Cost competitiveness of major airlines: an international comparison," Transportation Research Part A: Policy and Practice, Elsevier, vol. 32(6), pages 407-422, August.
- Barros, Carlos Pestana & Peypoch, Nicolas, 2009. "An evaluation of European airlines' operational performance," International Journal of Production Economics, Elsevier, vol. 122(2), pages 525-533, December.
- Morrell, Peter, 2007. "An evaluation of possible EU air transport emissions trading scheme allocation methods," Energy Policy, Elsevier, vol. 35(11), pages 5562-5570, November.
- Cui, Qiang & Li, Ye, 2015. "Evaluating energy efficiency for airlines: An application of VFB-DEA," Journal of Air Transport Management, Elsevier, vol. 44, pages 34-41.
- Ila Alam & Robin Sickles, 1998. "The Relationship Between Stock Market Returns and Technical Efficiency Innovations: Evidence from the US Airline Industry," Journal of Productivity Analysis, Springer, vol. 9(1), pages 35-51, January.
- Schmidt, Peter & Sickles, Robin C, 1984. "Production Frontiers and Panel Data," Journal of Business & Economic Statistics, American Statistical Association, vol. 2(4), pages 367-374, October.
- Macintosh, Andrew & Wallace, Lailey, 2009. "International aviation emissions to 2025: Can emissions be stabilised without restricting demand?," Energy Policy, Elsevier, vol. 37(1), pages 264-273, January.
- Arjomandi, Amir & Seufert, Juergen Heinz, 2014. "An evaluation of the world's major airlines' technical and environmental performance," Economic Modelling, Elsevier, vol. 41(C), pages 133-144.
- Motasemi, F. & Afzal, Muhammad T. & Salema, Arshad Adam & Moghavvemi, M. & Shekarchian, M. & Zarifi, F. & Mohsin, R., 2014. "Energy and exergy utilization efficiencies and emission performance of Canadian transportation sector, 1990–2035," Energy, Elsevier, vol. 64(C), pages 355-366.
- Good, David H. & Roller, Lars-Hendrik & Sickles, Robin C., 1995. "Airline efficiency differences between Europe and the US: Implications for the pace of EC integration and domestic regulation," European Journal of Operational Research, Elsevier, vol. 80(3), pages 508-518, February.
- Malina, Robert & McConnachie, Dominic & Winchester, Niven & Wollersheim, Christoph & Paltsev, Sergey & Waitz, Ian A., 2012. "The impact of the European Union Emissions Trading Scheme on US aviation," Journal of Air Transport Management, Elsevier, vol. 19(C), pages 36-41.
- Fare, Rolf, et al, 1989. "Multilateral Productivity Comparisons When Some Outputs Are Undesirable: A Nonparametric Approach," The Review of Economics and Statistics, MIT Press, vol. 71(1), pages 90-98, February.
- Alam, Ila M Semenick & Sickles, Robin C, 2000. "Time Series Analysis of Deregulatory Dynamics and Technical Efficiency: The Case of the U.S. Airline Industry," International Economic Review, Department of Economics, University of Pennsylvania and Osaka University Institute of Social and Economic Research Association, vol. 41(1), pages 203-218, February.
- Zou, Bo & Elke, Matthew & Hansen, Mark & Kafle, Nabin, 2014. "Evaluating air carrier fuel efficiency in the US airline industry," Transportation Research Part A: Policy and Practice, Elsevier, vol. 59(C), pages 306-330.
- Cui, Qiang & Kuang, Hai-bo & Wu, Chun-you & Li, Ye, 2014. "The changing trend and influencing factors of energy efficiency: The case of nine countries," Energy, Elsevier, vol. 64(C), pages 1026-1034.
- Robin Sickles & David Good & Lullit Getachew, 2002. "Specification of Distance Functions Using Semi- and Nonparametric Methods with an Application to the Dynamic Performance of Eastern and Western European Air Carriers," Journal of Productivity Analysis, Springer, vol. 17(1), pages 133-155, January.
- Greer, Mark R., 2008. "Nothing focuses the mind on productivity quite like the fear of liquidation: Changes in airline productivity in the United States, 2000-2004," Transportation Research Part A: Policy and Practice, Elsevier, vol. 42(2), pages 414-426, February.
- Oum, Tae Hoon & Yu, Chunyan, 1995. "A productivity comparison of the world's major airlines," Journal of Air Transport Management, Elsevier, vol. 2(3), pages 181-195.
- Lucas M Z Mendes & Georgina Santos, 2008. "Using Economic Instruments to Address Emissions from Air Transport in the European Union," Environment and Planning A, , vol. 40(1), pages 189-209, January.
- Derigs, Ulrich & Illing, Stefan, 2013. "Does EU ETS instigate Air Cargo network reconfiguration? A model-based analysis," European Journal of Operational Research, Elsevier, vol. 225(3), pages 518-527.
- David Good & M. Nadiri & Lars-Hendrik Röller & Robin Sickles, 1993.
"Efficiency and productivity growth comparisons of European and U.S. Air carriers: A first look at the data,"
Journal of Productivity Analysis, Springer, vol. 4(1), pages 115-125, June.
- Good, D.H. & Nadiri, M.I. & Roller, L.H. & Sickles, R., 1992. "Efficiency and Productivity Growth Comparisons of European and U.S. Air Carriers : A First Look at the Data," Working Papers 92-22, C.V. Starr Center for Applied Economics, New York University.
- Anger, Annela & Köhler, Jonathan, 2010. "Including aviation emissions in the EU ETS: Much ado about nothing? A review," Transport Policy, Elsevier, vol. 17(1), pages 38-46, January.
- Barros, Carlos Pestana & Wanke, Peter, 2015. "An analysis of African airlines efficiency with two-stage TOPSIS and neural networks," Journal of Air Transport Management, Elsevier, vol. 44, pages 90-102.
- Li, Ye & Wang, Yan-zhang & Cui, Qiang, 2015. "Evaluating airline efficiency: An application of Virtual Frontier Network SBM," Transportation Research Part E: Logistics and Transportation Review, Elsevier, vol. 81(C), pages 1-17.
- Tavassoli, Mohammad & Faramarzi, Gholam Reza & Farzipoor Saen, Reza, 2014. "Efficiency and effectiveness in airline performance using a SBM-NDEA model in the presence of shared input," Journal of Air Transport Management, Elsevier, vol. 34(C), pages 146-153.
- Barbot, Cristina & Costa, Ã lvaro & Sochirca, Elena, 2008. "Airlines performance in the new market context: A comparative productivity and efficiency analysis," Journal of Air Transport Management, Elsevier, vol. 14(5), pages 270-274.
- Wanke, Peter & Pestana Barros, Carlos & Chen, Zhongfei, 2015. "An analysis of Asian airlines efficiency with two-stage TOPSIS and MCMC generalized linear mixed models," International Journal of Production Economics, Elsevier, vol. 169(C), pages 110-126.
- Kopsch, Fredrik, 2012. "Aviation and the EU Emissions Trading Scheme—Lessons learned from previous emissions trading schemes," Energy Policy, Elsevier, vol. 49(C), pages 770-773.
- Albers, Sascha & Bühne, Jan-André & Peters, Heiko, 2009. "Will the EU-ETS instigate airline network reconfigurations?," Journal of Air Transport Management, Elsevier, vol. 15(1), pages 1-6.
- I. Ehrlich & Georges Gallais-Hamonno & Zh Liu & R. Lutter, 1994. "Productivy Growth & Firm Ownership : an Analytical & Empirical Investigation," Post-Print halshs-00276861, HAL.
- Zhang, Yue-Jun & Wei, Yi-Ming, 2010.
"An overview of current research on EU ETS: Evidence from its operating mechanism and economic effect,"
Applied Energy, Elsevier, vol. 87(6), pages 1804-1814, June.
- Yue-Jun Zhang & Yi-Ming Wei, 2009. "An overview of current research on EU ETS: Evidence from its operating mechanism and economic effect," CEEP-BIT Working Papers 3, Center for Energy and Environmental Policy Research (CEEP), Beijing Institute of Technology.
- Zhang, M. & Li, G. & Mu, H.L. & Ning, Y.D., 2011. "Energy and exergy efficiencies in the Chinese transportation sector, 1980–2009," Energy, Elsevier, vol. 36(2), pages 770-776.
- Sueyoshi, Toshiyuki & Goto, Mika, 2012. "Weak and strong disposability vs. natural and managerial disposability in DEA environmental assessment: Comparison between Japanese electric power industry and manufacturing industries," Energy Economics, Elsevier, vol. 34(3), pages 686-699.
- Atakelty Hailu & Terrence S. Veeman, 2001. "Non-parametric Productivity Analysis with Undesirable Outputs: An Application to the Canadian Pulp and Paper Industry," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 83(3), pages 605-616.
- Assaf, A. George & Josiassen, Alexander, 2012. "European vs. U.S. airlines: Performance comparison in a dynamic market," Tourism Management, Elsevier, vol. 33(2), pages 317-326.
- Bhadra, Dipasis, 2009. "Race to the bottom or swimming upstream: Performance analysis of US airlines," Journal of Air Transport Management, Elsevier, vol. 15(5), pages 227-235.
- Tone, Kaoru & Tsutsui, Miki, 2010. "Dynamic DEA: A slacks-based measure approach," Omega, Elsevier, vol. 38(3-4), pages 145-156, June.
- Lee, Boon L. & Worthington, Andrew C., 2014. "Technical efficiency of mainstream airlines and low-cost carriers: New evidence using bootstrap data envelopment analysis truncated regression," Journal of Air Transport Management, Elsevier, vol. 38(C), pages 15-20.
- Sebastián Lozano & Ester Gutiérrez, 2014. "A slacks-based network DEA efficiency analysis of European airlines," Transportation Planning and Technology, Taylor & Francis Journals, vol. 37(7), pages 623-637, October.
- Rolf Färe & Shawna Grosskopf, 2003. "Nonparametric Productivity Analysis with Undesirable Outputs: Comment," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 85(4), pages 1070-1074.
- Chiou, Yu-Chiun & Chen, Yen-Heng, 2006. "Route-based performance evaluation of Taiwanese domestic airlines using data envelopment analysis," Transportation Research Part E: Logistics and Transportation Review, Elsevier, vol. 42(2), pages 116-127, March.
- Ray, Subhash C & Mukherjee, Kankana, 1996. "Decomposition of the Fisher Ideal Index of Productivity: A Non-parametric Dual Analysis of US Airlines Data," Economic Journal, Royal Economic Society, vol. 106(439), pages 1659-1678, November.
- Sengupta, Jati K., 1999. "A dynamic efficiency model using data envelopment analysis," International Journal of Production Economics, Elsevier, vol. 62(3), pages 209-218, September.
- Oum, Tae Hoon & Fu, Xiaowen & Yu, Chunyan, 2005. "New evidences on airline efficiency and yields: a comparative analysis of major North American air carriers and its implications," Transport Policy, Elsevier, vol. 12(2), pages 153-164, March.
- Vespermann, Jan & Wald, Andreas, 2011. "Much Ado about Nothing? – An analysis of economic impacts and ecologic effects of the EU-emission trading scheme in the aviation industry," Transportation Research Part A: Policy and Practice, Elsevier, vol. 45(10), pages 1066-1076.
- Atakelty Hailu, 2003. "Nonparametric Productivity Analysis with Undesirable Outputs: Reply," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 85(4), pages 1075-1077.
- Wang, Wei-Kang & Lu, Wen-Min & Tsai, Chia-Jen, 2011. "The relationship between airline performance and corporate governance amongst US Listed companies," Journal of Air Transport Management, Elsevier, vol. 17(2), pages 148-152.
- Barros, Carlos Pestana & Couto, Eduardo, 2013. "Productivity analysis of European airlines, 2000–2011," Journal of Air Transport Management, Elsevier, vol. 31(C), pages 11-13.
- Tsai, Wen-Hsien & Lee, Kuen-Chang & Liu, Jau-Yang & Lin, Hsiu-Ling & Chou, Yu-Wei & Lin, Sin-Jin, 2012. "A mixed activity-based costing decision model for green airline fleet planning under the constraints of the European Union Emissions Trading Scheme," Energy, Elsevier, vol. 39(1), pages 218-226.
- Merkert, Rico & Hensher, David A., 2011. "The impact of strategic management and fleet planning on airline efficiency - A random effects Tobit model based on DEA efficiency scores," Transportation Research Part A: Policy and Practice, Elsevier, vol. 45(7), pages 686-695, August.
- Barros, Carlos P. & Liang, Qi Bin & Peypoch, Nicolas, 2013. "The technical efficiency of US Airlines," Transportation Research Part A: Policy and Practice, Elsevier, vol. 50(C), pages 139-148.
- Ouellette, Pierre & Petit, Patrick & Tessier-Parent, Louis-Philippe & Vigeant, Stéphane, 2010. "Introducing regulation in the measurement of efficiency, with an application to the Canadian air carriers industry," European Journal of Operational Research, Elsevier, vol. 200(1), pages 216-226, January.
- Cropper, Maureen L & Oates, Wallace E, 1992. "Environmental Economics: A Survey," Journal of Economic Literature, American Economic Association, vol. 30(2), pages 675-740, June.
- Veronique Distexhe & Sergio Perelman, 1994. "Technical Efficiency and Productivity Growth in an Era of Deregulation: the Case of Airlines," Swiss Journal of Economics and Statistics (SJES), Swiss Society of Economics and Statistics (SSES), vol. 130(IV), pages 669-689, December.
- Cornwell, Christopher & Schmidt, Peter & Sickles, Robin C., 1990.
"Production frontiers with cross-sectional and time-series variation in efficiency levels,"
Journal of Econometrics, Elsevier, vol. 46(1-2), pages 185-200.
- Cornwell, Christopher & Schmidt, Peter & Sickles, Robin C., 1989. "Production Frontiers With Cross-Sectinal And Time-Series Variation In Efficiency Levels," Working Papers 89-18, C.V. Starr Center for Applied Economics, New York University.
- Mallikarjun, Sreekanth, 2015. "Efficiency of US airlines: A strategic operating model," Journal of Air Transport Management, Elsevier, vol. 43(C), pages 46-56.
- Lu, Wen-Min & Wang, Wei-Kang & Hung, Shiu-Wan & Lu, En-Tzu, 2012. "The effects of corporate governance on airline performance: Production and marketing efficiency perspectives," Transportation Research Part E: Logistics and Transportation Review, Elsevier, vol. 48(2), pages 529-544.
- Capobianco, Heloisa Márcia Pires & Fernandes, Elton, 2004. "Capital structure in the world airline industry," Transportation Research Part A: Policy and Practice, Elsevier, vol. 38(6), pages 421-434, July.
- Tone, Kaoru, 2001. "A slacks-based measure of efficiency in data envelopment analysis," European Journal of Operational Research, Elsevier, vol. 130(3), pages 498-509, May.
- Chien, Taichen & Hu, Jin-Li, 2007. "Renewable energy and macroeconomic efficiency of OECD and non-OECD economies," Energy Policy, Elsevier, vol. 35(7), pages 3606-3615, July.
- Douglas W. Caves & Laurits R. Christensen & Michael W. Tretheway, 1984. "Economies of Density versus Economies of Scale: Why Trunk and Local Service Airline Costs Differ," RAND Journal of Economics, The RAND Corporation, vol. 15(4), pages 471-489, Winter.
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Keywords
Network slacks-based measure; Weak disposability; Strong disposability; Airline efficiency; European Union Emission Trading Scheme;All these keywords.
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