The hidden mediating role of innovation efficiency in coordinating development of economy and ecological environment: evidence from 283 Chinese cities.

The advancement of technological innovations may facilitate the coordinated development of the economy and ecological environment (EGE); however, few studies have noted the role of innovation efficiency (INEF) as a bridge between economic development and EGE. To fill in this gap, this paper adopts DMSP/OLS nighttime light data to measure the level of economic development and the improved data envelopment analysis model to measure INEF, establishing an index system to quantify EGE. Then we propose the panel threshold-mediating (PTM) model that combines the panel threshold model and the mediating effect model. On these bases, considering INEF as a mediator, we use this novel PTM model to empirically test the nonlinear relationship between economic development and EGE in 283 Chinese cities from 2003 to 2018. The results indicate that (1) while economic development can improve EGE, its positive impact on EGE differs with different INEF thresholds. A higher INEF threshold indicates a stronger positive effect of economic development on EGE. (2) For the entire sample, the mediating effect of INEF between economic development and EGE is not significant. However, after applying the PTM model, we found that the mediating effect of INEF was concealed by the sample population. (3) When INEF is lower than 0.2381, its complete mediating effect is verified. When INEF is higher than 0.2381, its mediating effect is not significant. On the contrary, economic development directly improves EGE. (4) Industrial agglomeration, the scale of government expenditure, residents' education level, degree of opening up, and transport infrastructure are all conducive to EGE. These findings can help cities at different INEF levels to achieve coordinated development of economy and EGE.