the uniqueness of the overall assurance interval for epsilon in dea models by the direction method

The role of non-archimedean ε in the dea models has been clarified, so that the associated linear programs can be infeasible (for the multiplier side) and unbounded (for the envelopment side) with an unsuitable choice of ε. this paper shows that the overall assurance interval for ε in dea models is unique by the concept of extreme directions. also, it presents an assurance value for ε using only simple computations on inputs and outputs of dmus.