改变政策实施时间的安慰剂检验的结果图非常奇怪，和平常看到的安慰剂检验结果相差很多，求助这是为什么
代码如下：

use "F:\innovation.dta",clear

mat b = J(500,1,0)
mat se = J(500,1,0)
mat p = J(500,1,0)

forvalues i=1/500{
use "F:innovation.dta", clear
xtset daima year
drop if treat<1
sample 1, count by(daima)
keep daima year
rename year policy_year
save match_id.dta, replace
merge 1:m daima using "F:innovation.dta"
xtset daima year
gen treat2 = (_merge == 3)
gen period = (year >= policy_year)
gen dd = treat2*period
reg innovation dd lnpergdp third finance lnpeople i.daima i.year
mat b[`i',1] = _b[dd]
mat se[`i',1] = _se[dd]
mat p[`i',1] = 2*ttail(e(df_r), abs(_b[dd]/_se[dd]))

上面三个图分别修改了控制组、开始年份和实验组&开始年份