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

This paper, by using conditional directional distance functions as introduced by Simar and Vanhems [J. Econometrics 166 (2012) 342-354] modifies the model by Färe and Grosskopf [Eur. J. Operat. Res. 157 (2004) 242-245], examines the link between regional environmental efficiency and economic...