6.1. Conclusions
This paper develops integrated DEA (IDEA) models, under constant-returns-to-scale (ICCR model) and variable-returns-to-scale (IBCC model) technologies, to measure the overall efficiency and separate efficiencies for non-storable commodities, from various aspects of technical efficiency, service effectiveness, and technical effectiveness. Some major findings can be concluded as follows:
(1) The proposed IDEA model, either ICCR or IBCC, is proven with rationality and uniqueness properties. The property of rationality suggests that the scores obtained from this integrated model are efficient values rather than meaningless figures. The property of uniqueness guarantees that the efficiency scores obtained from this model are global maximum rather than local maximum.
(2) Our proposed IDEA models can be employed to measure the overall efficiency of non-storable commodities such as transportation services.
The applicability of the proposed IDEA model has been demonstrated by a case study, from which the IDEA model has revealed higher discrimination power than the conventional separated DEA models.
(3) Compared with conventional separated DEA model, the proposed IDEA model can explain for non-storable commodities more explicitly. Because the IDEA model can jointly account for the production and sale departments of non-storable commodities, it is superior to conventional DEA models.
6.2. Suggestions
Some directions for future studies can be identified as follows.
(1) The weight analysis of the proposed IDEA model is worthy to make a further study because the weight in this study is an exogenous variable, not an endogenous variable. One could add the weight variable into the integrated DEA model and let the model decide the optimal weight for each department.
(2) An additive form of proposed IDEA model is derived in this paper, other forms of IDEA models or even multi-objective IDEA models deserve further exploration.
(3) The present paper only demonstrates the overall efficiency measure for two departments -- production (technical efficiency) and sale (service effectiveness). The proposed IDEA model can easily be extended to evaluate the overall performance of an organization with more than two departments that are vertically and/or horizontally coordinated, e.g., the supply chain managing of a firm, the mails processing of the post office, among others.
(4) More applications to other non-storable cases with the proposed IDEA model and more comparisons with other types of DEA models are also worthy of further study.
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