A New Gradual Efficiency Improvement Model for Environmental Assessment Projects Decision Making Units on the Scale Efficiency Frontier in DEA

When Data Envelopment Analysis is used for evaluate the decision making units, the efficient target identified by the selected DEA model can be very far away. Therefore, to reach the target it requires large reduction in inputs and large increase in outputs. In such cases gradual improvement strategy is a useful tool which consists of a sequence of targets that each of them is easily achievable from the previous one. In the variable return to scale technology there is deferent between technical efficient and scale efficient units so that scale efficient units have optimal size. In the field of gradual improvement strategy , Lozano and Villa proposed two model, the first one for inefficient units which determines successive intermediate targets leading units to become technical efficient, and secondly for those units that are technical efficient but not scale efficient which computes a sequence of targets on the surface towards obtaining global efficiency, In other words initially inefficient units improve to the technical efficiency frontier and in the second period, by another model units move to the scale efficient targets. In this paper we suggest that a new gradual improvement model used for both inefficient units and efficient units that are not scale efficient, improved them towards the scale efficient target directly, i.e. in both cases the new model moves units to the global efficiency frontier in direction of scale efficiency by determining successive targets obtained by placing bounds on the rates of changes in inputs and outputs in the fewer steps.