Unified efficiency of coal mining enterprises in China: An analysis based on meta-frontier non-radial directional distance functions

Evaluating the energy efficiency of coal mining enterprises (CME) is a key factor in formulating science-based energy saving and emission reduction policies. Based on a unique micro-level dataset from 2008 to 2011, this study uses meta-frontier non-radial directional distance functions (MNDDF) to evaluate the unified efficiency of China's CME from static and dynamic perspectives. The results show that: (1) the unified efficiency of Chinese CME is extremely low, with most values ranging between 0.1 and 0.3. Although there is heterogeneity among the unified efficiencies of CME under different benchmark frontiers, all of the efficiency values are small and there is much room for improvement. (2) From an enterprises perspective, private CME, small CME and CME in the western region have relatively low unified efficiency, and the proportion of inefficient CME in Hebei, Liaoning, Inner Mongolia, Heilongjiang, Shanxi, Henan, Hunan and Guizhou is relatively high. (3) Due to the 2008 financial crisis, the unified efficiencies of the CME in the eastern and central regions first decrease and then increase during 2008-2011, whereas those in the western region show a fluctuating downward trend. Moreover, the unified efficiency of the state-owned CME and large CME increased slightly during 2008-2011, while that of the private CME and small CME decreased significantly. (4) The Meta-frontier Malmquist unified indices (MMUEI) and their decomposed indicators exhibit large variations across regions and enterprise types during the sample period.