A Layer DEA Model for Measuring and Improving the Efficiency in the Presence of Special Decision Making Units

In the evaluation of non-efficient units by Data Envelopment Analysis (DEA) referenced Decision Making Units (DMU s) have an important role. Unfortunately DMU s with extra ordinary output can lead to a monopoly in a reference set, the fact called abnormality due to the outliers data. In this paper, we introduce a DEA model for evaluating DMU s under this circumstance. The layer model can result in a ranking for DMU s and obtain an improving strategy leading to a better layer.