Table 7.

Results of core explanatory variable substitution test.

Variables	Model 6	Model 7	Model 8	Model 9
Operating revenue	0.004*** (8.65)	0.006*** (4.58)	0.007*** (4.65)	0.004*** (5.52)
Regional development level		0.061*** (6.62)
Labor union			0.115*** (5.57)
Workers’ congress				0.041** (2.41)
Operating revenue × Regional development level		−0.001** (−1.99)
Operating revenue × Labor union			−0.004** (−2.38)
Operating revenue × Workers’ congress				−0.001 (−1.13)
Control variables	Yes	Yes	Yes	Yes
R 2	0.086	0.138	0.139	0.137
Adj. R2	0.086	0.136	0.137	0.135
F-value	92.72***	67.28***	67.57***	66.84***

*p < 0.1, **p < 0.05, ***p < 0.001.