政策实施前(policy = 0)

政策实施后(policy = 1)

Difference

处理组(treat = 1)

${\beta }_0+{\beta }_1$

${\beta }_0+{\beta }_1+{\beta }_2+{\beta }_3$

$\Delta fd{i}_t={\beta }_2+{\beta }_3$

控制组(treat = 0)

${\beta }_0$

${\beta }_0+{\beta }_2$

$\Delta fd{i}_0={\beta }_2$

DID

—

—

$\Delta \Delta fd{i}_0={\beta }_3$