Is the High-Speed Rail Opening Environmentally Friendly? Taking the Difference-in-Differences Test in Jiangsu, China

Table 3

Common trend test.

	(1)
	Goodday
Central	−2.146; (0.495)
PGDP	0.001; (0.001)
PGDP^2	−7.90×10^−9; (3.35×10^−9)
T3	0.678; (0.394)
PI	−0.003; (0.002)
U	1.107; (0.300)
FDI	−1.574; (0.469)
Constant	6.514; (0.706)
Time effect	Control
Urban effect	Control
Within R^2	0.282
Samples	234

, , and indicate the level of significance through 1%, 5%, and 10%, respectively.