xtset n year
panel variable: n (strongly balanced)
time variable: year, 1994 to 2015
delta: 1 unit
. gen lnfm=log(fm)
(7 missing values generated)
. by n:ipolate lnfm year,gen(lnfm1)
(7 missing values generated) 不太明白为什么我对面板数据用插值函数插值后,为什么还是有缺漏值??