The Modified Two-Phase Approach to Find Non-negative Target for Inefficient Units in the DEA with Negative Data

In conventional DEA models, all data are always considered to be non-negative. While, in many cases, one or more inputs and/or outputs are assigned negative value. Up to now, many approaches have been presented to evaluate efficiency of DMUs (Decision Making Units) and to obtain target for inefficient units with the presence of negative data. In this paper, at first a brief review of these methods is presented. In all of these methods, there is no guarantee that the obtained target has non-negative value, recently, Kazemi et al [1] presented two-phase approach in which the obtained target is non-negative, and then the modified two-phase method is suggested to improve the disadvantages of Kazemi's method . Next, these methods are compared by presenting examples.