$\Delta D_{it}=\alpha +\beta DE{F}_{it}+\gamma DE{F}_{it}^2+{\epsilon }_{it}$

sample 1 (1)

sample 2 (2)

β

−0.125220****

(0.0014)

−0.182271***

(0.0000)

γ

−1.82E−12

(0.4748)

−4.19E−13

(0.8751)

N

153

153

R²

0.675767

0.743556

F-test

3.821031***

5.316015***