WASET
    Alexander Y. Vaninsky,  Environmental Performance of the United States Energy Sector: A DEA Model with Non-Discretionary Factors and Perfect Object.   journal   = {International Journal of Energy and Environmental Engineering}, [online]. World Academy of Science, Engineering and Technology.
    June 2009, vol. 30(6). 126 - 131
    [viewed 08 May 2024]. Available from: https://publications.waset.org/pdf/3241.