ima at aqua.dtu.dk
Tue Jun 3 17:49:25 CEST 2008
I have set up a linear mixed model:
using the nlme library.
When I try to make the error structure group specific using
the model cannot converge using the default settings:
"nlminb problem, convergence error code = 1
message = iteration limit reached without convergence (9)"
However, if I modify the maximum number of iterations in lmeControl
(both maxIter and msmaxIter are set to 500), then the model can indeed
The problem is then that I cannot get the confidence intervals for the
variance-covariance components, but this error message appears:
"Cannot get confidence intervals on var-cov components: Non-positive
definite approximate variance-covariance"
On the other hand, model comparison shows that the model with the
heterogenous variances is superior.
So, I am wondering if the lmeControl modification can invalidate the
model results and if I should use it at all.
(Please let me know if you need any more details about the model)
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