xtset city year
xtreg lncrime sreduca2 srsocial2  avGDP2 lagunemploy, re robust
outreg2 using "outreg2-pd", word excel replace
xtreg lncrime sreduca2 srsocial2  avGDP2 lagunemploy, fe robust
outreg2 using "outreg2-pd", word excel append
xi: reg lncrime sreduca2 srsocial2 laglnunemploy avGDP2 i.city, robust
outreg2 using "outreg2-pd", word excel append
xi: reg lncrime sreduca2 srsocial2 laglnunemploy avGDP2 i.city, robust
outreg2 using "outreg2-pd", word excel drop(_I*) append
xi: reg lncrime sreduca2 srsocial2 laglnunemploy avGDP2 i.year, robust
outreg2 using "outreg2-pd", word excel append
xi: reg lncrime sreduca2 srsocial2 laglnunemploy avGDP2 i.year, robust
outreg2 using "outreg2-pd", word excel drop(_I*) append

输入上式后发现带一颗星的结果依然存在。请问是何原因？求大神指教！