forvalues i=1(1)500 {
use "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta",clear
save did1_data,replace
use did1_data,clear
keep id year lnSO2
save did_data,replace
use did_data,clear
bysort id: keep if year == 2018
sample 132, count
keep id
save temp,replace
use did1_data,clear
merge m:1 id using temp
drop treatment
gen treatment=(_merge==3)
drop _merge
save did1_data,replace
use did1_data,clear
gen did_0=treatment*post
sort id
xi:areg lnSO2 did days2 secdgdp lnpop fislevel lnpgdp lniforinv lntech i.year, absorb(city) cluster(id)
parmest,format (estimate min95 max95 %8.2f p %8.3f) saving("temp1.dta", replace)
use "temp1.dta", clear
keep if parm=="did_0"
append using "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta"
save "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta",replace
}
erase "temp1.dta"
use "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta",clear
drop if estimate==.
save "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta",replace
use "D:\Evelyn\研究生课程\毕业论文\环保税\实证\环保会与空气污染 - 副本.dta",clear
kdensity estimate,xline(0) ytitle("概率密度") xtitle("系数估计值") saving("图2.png",replace)