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Corrected repost: Two general questions about xt commmands and re / fe


From   "Mark Marshall" <mrmarsh@woosh.co.nz>
To   <statalist@hsphsun2.harvard.edu>
Subject   Corrected repost: Two general questions about xt commmands and re / fe
Date   Sun, 12 Apr 2009 09:37:56 +1200

Hi

I am using Stata 9.2 on windows.

I am fitting an xtpoisson model to unbalanced panel data (n counts of death
over T months), with a grouping variable called unit that signifies the ICU
where the data come from. E.g

obs_rrt	T	unit
0		5	4
3		6	4
2		7	4
4		8	4
3		9	4
1		10	4
3		2	3
1		3	3
1		4	3
1		5	3
0		6	3
1		7	3

Question 1.

When I specify 

tis T

my understanding is that this does not explicitly model T in the model (I
want to model the death rate in relationship to time, amongst other things),
and I would have to specify T in the command line to do this. Is this
correct?

Question 2.

I would like to specify T and some other exposure covariates as fixed
effects, and unit as a random effect in the model. If I specify all of these
as independent variables in the command line, and then use the re option,
how can I tell which is modelled as fixed, and which is modelled as random? 

Thanks,

Mark Marshall



 





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