在做平行趋势检验之前我先试了一下政策的实行是否是有效的
做了下面的do命令
xtset city year
gen year14=1   //政策在2014年实行
replace year14=0 if year<=2014

gen yuebei=0  //政策中，粤北包括韶关、梅州、清远、河源、云浮
replace yuebei=1 if city==440200|city==441400|city==441600|city==441800|city==445300
gen yuebei_yr=yuebei*year14  //生成粤北和时间的交互项

gen zhu=0  //政策中，珠三角包括广州、深圳、珠海、佛山、江门、东莞、中山、惠州、肇庆
replace zhu=1 if city==440100|city==440300|city==440400|city==440600|city==441300|city==440700|city==441900|city==442000|city==441200
gen zhu_yr=zhu*year14  //生成珠三角和时间的交互项

gen yuedongxi=0  //政策中，粤东包括汕头、汕尾、潮州、揭阳，粤西包括湛江、阳江、茂名
replace yuedongxi=1 if city==440800|city==440900|city==441700|city==440500|city==441500|city==445100|city==445200
gen yuedongxi_yr=yuedongxi*year14  //生成粤东西和时间的交互项

gen treated=0  //粤北为参照组，粤东西和珠三角地区是实验组
replace treated=1 if city==440800|city==440900|city==441700|city==440500|city==441500|city==445100|city==445200|city==440100|city==440300|city==440400|city==440600|city==441300|city==440700|city==441900|city==442000|city==441200

reg water yuebei zhu yuebei_yr zhu_yr year14 i.city i.year,r
reg gas yuebei zhu yuebei_yr zhu_yr year14 i.city i.year,r
reg dust yuebei zhu yuebei_yr zhu_yr year14 i.city i.year,r
//DID回归

reg water yuebei yuedongxi yuebei_yr yuedongxi_yr year14 i.city i.year,r
reg gas yuebei yuedongxi yuebei_yr yuedongxi_yr year14 i.city i.year,r
reg dust yuebei yuedongxi yuebei_yr yuedongxi_yr year14 i.city i.year,r
//DID回归

得到了下面的结果 所以回归分析的结果应该是
政策对粤东西地区的dust、gas和water显著有效，对珠三角的dust/gas/water是没有效果的？