st: Nº of Observations in Probit regressions

[SMAC <s.afcha@ub.edu>]

Dear Statalisters,

I have a little doubt about the probit's output "Nº Obs."  what does it 
means exactly?
I have an unbalanced  panel with 5120 obs. (8 years x 640 firms in 
average), but when I run a probit regression (with probit command, not 
xtprobit)
the Nº obs specified in the output is 2225. What happens with the rest 
of observations? are they dropped due to missing values in independent 
variables?
Dependent Variable has not missing values, but among independents 
variables, there is several variables with missing data.
I would really appreciate your help,

Sergio


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