Dear all,

I am running the following code:

. xtset id year

. xi: xtivreg2 `t' (`z'=instrument_p) i.year i.ccode if drop10_ncidef`y'!=1 & `x'==1 & `s'==1 , fe first cluster (ccode)
panel variable: id (unbalanced)
time variable: year, 2006 to 2015, but with gaps
delta: 1 unit
i.year _Iyear_2006-2015 (naturally coded; _Iyear_2006 omitted)
i.il_kodu _Iil_kodu_1-81 (naturally coded; _Iil_kodu_1 omitted)

Warning - singleton groups detected. 19125 observation(s) not used.



However the warning tells that covariance matrix is not of full rank, possibly resulting from singletons. Therefore, I want to locate all singletons and I am wondering whther there is any way to locate those 19125 variables in my sample. I have tried to use e(sample) as suggested in previous postings but it did not help me to find out /locate singletons.

Many thanks
Nazlı