An improvement to the cost efficiency interval: A DEA-based approach

The purpose of this paper is to improve the cost efficiency interval of a decision making unit by adjusting its observed inputs and outputs. We first propose a DEA-based model with an interval efficiency in which the lower bound and upper bound of this interval, are respectively, the efficiency obtained from optimistic and pessimistic viewpoints. Then, units which are not prevail as cost efficient, are improved so that their lower bounds of cost efficiency become as large as possible and their upper bound attain the maximum value 1. The particular application area investigated is that involving the gas companies of Iran.