@article{Charnes1978,
author = {Charnes, A. and Cooper, W.W. and Rhodes, E.},
title= {Measuring the efficiency of decision units},
year = {1978},
doi = {10.1016/0377-2217(78)90138-8},
journal = {European Journal of Operational Research},
volume = {2},
number = {6},
pages = {429--444},
}