Directional distance function is the generalization of radial model in data envelopment analysis. It has the capacity of dealing with undesirable outputs, but the problem is that it has no unit-invariant measurement of efficiency, which hampers its application to empirical studies. Data...

Directional distance function is the generalization of radial model in data envelopment analysis. It has the capacity of dealing with undesirable outputs, but the problem is that it has no unit-invariant measurement of efficiency, which hampers its application to empirical studies. Data...