Abstract
Prior research (Banker and Chang in Eur J Oper Res 175: 1311–1320, 2006) has found that super-efficiency based procedures are effective in identifying outliers, but not in ranking efficient units. In this paper, we investigate why the procedures failed to rank efficient units satisfactorily and examine the performance of super-efficiency procedures in different “regions” of production set. We find that the unsatisfactory results mainly originate from the “left corners” of DMUs, those units with relatively smaller values. We further examine the effect of different noise levels on outlier detection using the BG procedure (Banker and Gifford in A relative efficiency model for the evaluation of public health nurse productivity. Mimeo, Carnegie Mellon University, Pittsburgh, 1988). Our results show that the BG procedure is more effective when the noise level is high. We conduct extensive simulation experiments by considering different production functions (Cobb–Douglas and Polynomial), different DEA formulations (BCC and CCR) and different returns-to-scale (CRS and NIRS) assumptions. Our simulation results confirm that the findings in Banker and Chang (2006) are robust under different DEA formulations, production functions and returns to scale assumptions.
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Notes
Subsequently, Wilson (1995) also suggested exactly the same use of the super-efficiency model for identifying outliers.
While the super-efficiency model is specified in (1) for the BCC model, similar models can be specified corresponding to other DEA specifications. The CCR (Charnes et al. 1978) super-efficiency specification is the same linear program as in (1) except that the constraint in (1c) is deleted. The NDRS (non-decreasing returns to scale) specification is the same linear program as in (1) except that the constraint in (1c) is a less-than-or-equal-to (=) constraint instead of an equality (=) constraint. The NIRS (non-increasing returns to scale) specification is the same linear program as in (1) except that the constraint in (1c) is a greater-than-or-equal-to (=) constraint instead of an equality (=) constraint.
Observe that there always exists an optimal solution to (2) with either \({\uplambda }_\mathrm{k}^*=0\) or \({\uplambda }_\mathrm{k}^*=1\).
We chose the shifted Cobb–Douglas because it provides a parsimonious parametric form that exhibits both increasing and decreasing returns to scale for \(\alpha _i >0.\)
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We acknowledge many helpful discussions with W.W. Cooper on this subject.
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Banker, R.D., Chang, H. & Zheng, Z. On the use of super-efficiency procedures for ranking efficient units and identifying outliers. Ann Oper Res 250, 21–35 (2017). https://doi.org/10.1007/s10479-015-1980-8
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DOI: https://doi.org/10.1007/s10479-015-1980-8