## 4 Empirical Results
### Heterogeneity Impact on Policy Effect
#### 4.5.3 DDD Mechanism Test  
By successively using each control variable as an explanatory variable, we study the conduction mechanism of the economic differences and industrial differences on the carbon reduction effect and economic effect. According to the analysis in Table 10, the following is found. (1) From the coefficients of the Z-values, it is found that the causes of the carbon reduction effect in the ETS pilot provinces are mainly from the reductions of the industrialization rate, carbon intensity, and energy structure and the increases of the research structure and research intensity. Furthermore, the economic effect in the ETS pilot provinces is due to the increased capital, employment and energy consumption. (2) According to the coefficients of Z*if_econ, Z*if_indu, Z*if_serv, and Z*if_cons, compared with the provinces with lower levels of economic and industrial development, the population size, carbon intensity and per capita GDP have positive effects on the carbon emissions in the provinces with higher levels of these variables. Further, the intensity of the environmental pollution controls, research structure and research intensity have negative effects on carbon emissions in the provinces with higher levels of \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Inc**} & \multicolumn{2}{c}{**if\_indu**} & \multicolumn{2}{c}{**if\_serv**} & \multicolumn{2}{c}{**if\_cons**} \\ \cline{2-7}  & **m1** & **m2** & **m3** & **m4** & **m5** & **m6** \\ \hline \(Z\)*if\_ & 0.0622 (0.84) & 0.058 (1.87) & \(-\)0.298 (\(-\)0.85) & \(-\)0.488 *** (\(-\)5.14) & 0.097 (0.69) & 0.081 * (1.79) \\ \(Z\) & \(-\)0.141 * (\(-\)1.83) & \(-\)0.124 * (\(-\)1.84) & \(-\)0.116 (\(-\)0.68) & 0.267 *** (4.52) & \(-\)0.318 * (\(-\)1.87) & \(-\)0.121 * (\(-\)1.80) \\ Inp & & 2.390 *** (40.7) & 2.427 *** (54.75) & & 2.431 *** (46.16) \\ us & & 0.019 *** (8.99) & & 0.018 *** (8.33) & 0.020 *** (9.36) \\ a & & 0.165 *** (9.76) & & 0.177 *** (9.53) & & 0.172 *** (9.19) \\ is & & 0.012 *** (7.23) & & 0.014 *** (8.28) & & 0.014 *** (8.61) \\ ci & & 0.175 *** (9.46) & & 0.171 *** (9.33) & & 0.164 *** (9.01) \\ energy & & 0.007 *** (7.23) & & 0.007 *** (7.00) & & 0.007 *** (6.66) \\ environs & & \(-\)0.070 *** (\(-\)2.62) & & \(-\)0.078***(\(-\)2.87) & & \(-\)0.071 *** (\(-\)2.88) \\ rs & & \(-\)0.164 *** (\(-\)2.01) & & \(-\)0.124 *(\(-\)1.82) & & \(-\)0.026 * (\(-\)1.81) \\ ri & & \(-\)0.115 *** (\(-\)5.25) & & \(-\)0.093 *** (\(-\)4.44) & & \(-\)0.045 * (1.92) \\ control & no & yes & no & yes & no & yes \\ province & yes & yes & yes & yes & yes & yes \\ time & yes & yes & yes & yes & yes & yes \\ R-square & 0.570 & 0.949 & 0.506 & 0.950 & 0.435 & 0.952 \\ \hline \hline \end{tabular} \({}^{*}\)_p_ \(<\) 0.05, **\(p\)\(<\) 0.01, *** \(p\)\(<\) 0.001.  
\end{table} 
Table 8: Emission reduction effect of industrial development differences. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Ingdp**} & \multicolumn{2}{c}{**if\_indu**} & \multicolumn{2}{c}{**if\_serv**} & \multicolumn{2}{c}{**if\_cons**} \\ \cline{2-5}  & **m1** & **m2** & **m3** & **m4** & **m5** & **m6** \\ \hline \(Z\)*if\_ & \(-\)0.020 (-0.20) & \(-\)0.033 (\(-\)0.21) & \(-\)0.019 (\(-\)0.18) & \(-\)0.027 (\(-\)0.28) & \(-\)0.150 (\(-\)0.48) & \(-\)0.169 (\(-\)1.27) \\ Z & 0.012 (0.70) & 0.128 (1.23) & 0.004 (1.53) & 0.080 ** (2.08) & 0.129 (1.620) & 0.193 ** (2.02) \\ Ink & & 0.602 (\(-\)21.26) & & 0.594 * (21.19) & & 0.534 * (19.54) \\ Inl & & 0.337 *** (14.48) & & 0.315 *** (13.61) & & 0.381 *** (15.90) \\ Ine & & 0.209 *** (8.47) & & 0.188 *** (7.81) & & 0.275 *** (11.08) \\ control & no & yes & no & yes & no & yes \\ province & yes & yes & yes & yes & yes & yes \\ time & yes & yes & yes & yes & yes & yes \\ R-square & 0.532 & 0.962 & 0.568 & 0.967 & 0.451 & 0.967 \\ \hline \hline \end{tabular} \({}^{*}\)_p_ \(<\) 0.05, **\(p\)\(<\) 0.01, *** \(p\)\(<\) 0.001.  
\end{table} 
Table 9: Economic effect of industrial development differences. economic and industrial development.