Reddy, G.Thirupati. “Efficiency Scores Analysis of Coal Mines Using IRS, DRS and Cross Efficiency Models”. Journal of Advance Research in Mechanical and Civil Engineering (ISSN: 2208-2379) 2, no. 2 (February 28, 2015): 01–07. Accessed May 18, 2024. https://nnpub.org/index.php/MCE/article/view/367.