*安慰剂代码
use data,clear
cap erase "simulations.dta"
permute DID beta=_b[DID] se=_se[DID] df=e(df_r),reps(500) seed(123) saving("simulations.dta"):reghdfe $y $x $control ,absorb(proid year) vce(cluster proid)
use "simulations.dta",clear
gen t_value=beta/se
gen p_value=2*ttail(df,abs(beta/se))
dpplot beta,xtitle("Estimator",size(*0.8)) xlabel(,format(%4.3f) labsize(small)) ytitle("Density",size(*0.8)) ylabel(,nogrid format(%4.3f) labsize(small)) note("") caption("") graphregion(fcolor(white))

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