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st: problem with factor variables in RE probit


From   "Liberini, Federica" <F.Liberini@warwick.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: problem with factor variables in RE probit
Date   Tue, 27 Sep 2011 12:41:59 +0100

Dear listers, 

I am having problems using the factor variables in a RE probit model. 

My "group" variable is a categorical that can take up to 3 different
values. My "X" variable is a continuous. 
What I did was to compare two regressions:

tab group, gen(group)
gen gr1_x=group1*x
gen gr2_x=group2*x

xtprobit y x group1 group2 gr1_x gr2_x xbar zbar, re

compared to 

xtprobit y b3.group##c.x xbar zbar, re

(the xbar and zbar variables are for the RE specification)

Now, before running the two regressions I made sure that the virtual
variables generated by b3.group##c.x were identical to the varlist x
group1 group2 gr1_x gr2_x . I did this by typing

list x group1 group2 gr1_x gr2_x  b3.group##c.x in 1/100

and they were!

So why is that the two regression command return different outcomes?

Many thanks
Federica

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