This paper proposes a conditional directional distance function estimator in order to examine the link between regional environmental efficiency and GDP per capita levels. As an illustrative example we apply our model to US regional data revealing an inverted ‘U’ shape relationship between...

The paper applies time-dependent conditional frontier estimators in order to examine the effect of human capital on countries’ economic efficiency levels. Specifically, time-dependent conditional full and partial efficiency measures are applied to a sample of 123 countries for the period of...