About stci command

#1
Dear experts,
After using stci command,

. stci if factorA==0, by(factorB)

failure _d: pfsevent
analysis time _t: (pfsexitdate-origin)/365.25
origin: time dateofdiagnosis
id: id

| no. of
factorB | subjects 50% Std. Err. [95% Conf. Interval]
-------------+-------------------------------------------------------------
1 | 9 5.054073 1.620295 .536619 .
2 | 13 1.585216 .3395563 .44627 3.66051
-------------+-------------------------------------------------------------
total | 22 2.047912 1.240971 .991102 5.05407


Why was the 95% confidence interval of factorB value 1 absent??
Thanks

Regards
Michael