Chodakowska, Ewa, and Joanicjusz Nazarko. “Environmental DEA Method for Assessing Productivity of European Countries”. Technological and Economic Development of Economy 23, no. 4 (June 16, 2017): 589-607. Accessed July 2, 2024. https://aviation.vgtu.lt/index.php/TEDE/article/view/652.