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st: AW: xtmixed with random slope - STATA 11 vs STATA 10

From   "Martin Weiss" <>
To   <>
Subject   st: AW: xtmixed with random slope - STATA 11 vs STATA 10
Date   Thu, 29 Oct 2009 09:32:42 +0100


what happens when you fit this model?

webuse nlswork, clear
xtmixed ln_w grade age c.age#c.age ttl_exp tenure c.tenure#c.tenure || id:
grade, cov(unstruct) mle

Note that your command will not run as shown, as -xt- would have to be -xi-
for it to work. Even -xi- is no longer the best solution in Stata 11. See
[u], 11.4.3 for factor variables...


-----Ursprüngliche Nachricht-----
[] Im Auftrag von Ada Lo
Gesendet: Donnerstag, 29. Oktober 2009 02:38
Betreff: st: xtmixed with random slope - STATA 11 vs STATA 10

Hi there,

I started using STATA SE/10 for Mac and then upgraded to STATA SE/11.
I was able to use xtmixed to fit a random intercept random slope model
with unstructured covariance in STATA 10 but when I ran the exact same
command in the same dataset in STATA 11, the iteration would not stop.
Basically, I stopped it when it reached 100... Does anyone know why
and how to make it work in STATA 11?

The basic model is - xt: xtmixed Memory age agesq i.retest i.dropout
|| StudyID: i.retest, cov(unstructured) mle

By the way, I do notice that the covariance structure could be the
problem because when cov(independent) was specified, both STATA 10 and
11 could generate the model. However, because these are longitudinal
data (3 repeated measurements over 8 years with roughly 490
participants) and the data are expected to correlate within
individuals, I thought cov(unstructured) would be the best option
given that autogressive covariance structure is not available in

Thanks in advance!

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