Unit Root Test Panel Data

[Germain Lankoande]

Hi!

I went help for Unit Root Test for Panel Data.

I do Unit Root Test and the result is that.

. xtunitroot ips L.FD_FI_IX

Im-Pesaran-Shin unit-root test for L.FD_FI_IX
---------------------------------------------
Ho: All panels contain unit roots Number of panels = 39
Ha: Some panels are stationary Avg. number of periods = 36.97

AR parameter: Panel-specific Asymptotics: T,N -> Infinity
Panel means: Included sequentially
Time trend: Not included

ADF regressions: No lags included
------------------------------------------------------------------------------
Fixed-N exact critical values
Statistic p-value 1% 5% 10%
------------------------------------------------------------------------------
t-bar -1.5916 (Not available)
t-tilde-bar -1.4894
Z-t-tilde-bar -0.2639 0.3959
------------------------------------------------------------------------------

I don't understand why I have (Not available).

Thanks.