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st: xtmixed and unstructured covariance uncovergence


From   "moleps islon" <[email protected]>
To   [email protected]
Subject   st: xtmixed and unstructured covariance uncovergence
Date   Fri, 16 Jan 2009 21:26:27 +0100

Dear listmembers,
I'm investigating the effect of inclination (Inc) on bloodpressure
(Bp) in different people(Id). I've got 15 min of averaged 6 sec epochs
(150 measurements) at each level of Inc (total of 6 levels).  Bp at
each Inc and within each Id are obviously not independent, so I'm
trying to fit a model---.xtmixed Bp Inc || Id:Inc, cov(unstr)-- .
However a warning appears: Warning: convergence not achieved;
estimates are based on iterated EM. Is this due to the correlation
between the measurements and insufficient # of Id ?? In that case how
can I do a poweranalysis for this problem?

Regards,
Moleps
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