Determination of right/left return to scale in two-stage processes based on dual simplex

As a non-parametric method of relative efficient measurement of a group of decision-making units (〖DMU〗_s), Data Envelopment Analysis (DEA) is one of the most important tools in efficiency computation. One of the main concerns dealt with in DEA is dealing with return to scale in two-stage processes in which, produced outputs of the first stage inputs are used as inputs for the second stage. The outputs of the first stage are considered as intermediate products. Therefore, the second stage uses these intermediate products for producing the outputs of the same stage. Based on this construction, the total process can be analyzed for efficiency production from two sub-processes. In this paper, a new model is proposed that eliminates the defections of the previous models and is used to determine the right and left return to scale in two-stage processes of decision-making units.