The key unifying conceptual tool of this important entry in the study of
efficiency and productivity is the directional distance function. In
this book, the authors take up this new performance measure while also
maintaining their "traditional" axiomatic production theoretic approach.
The directional distance function includes traditional distance
functions and efficiency measures as special cases providing a unifying
framework for existing productivity and efficiency measures. As a
generalization of the traditional distance functions, it turns out to be
a dual to the profit function, opening a range of new tools for
empirical and theoretical research.