变量

(1)

(2)

(3)

Upgrade

Treat × Time

0.072^***

0.089^***

0.018

(3.14)

(3.84)

(0.88)

Constant

−2.553^***

−2.297^***

−0.770

(−10.60)

(−9.33)

(−1.36)

Control_Var

YES

YES

YES

YearFE

YES

YES

YES

AreaFE

YES

YES

YES

Observations

15,376

10,945

17,242

Adjusted R-squared

0.750

0.747

0.914