st: stata drops variable at random

[Marck Bulter <177316mb@student.eur.nl>]

Dear all,

Currently I am working on a panel data regression. Main problem is that 
Stata drops variables at random immediately after a performed regression.
For example if the following regression is performed:

xtivreg pstrmon price mat age coup pstrmonprev pstrprev intr ivol compl 
(precmon = price mat age coup pstrmonprev pstrprev intr ivol compl 
precmonprev)

Stata drops often one of the above variables, or the ID-var or the Time-Var

Any help would be very much appreciated, not much hair left,

Kind regards,
Marck Bulter




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