Good R-users,
I have difficulties accessing the variance components for an lme fit when the
variance covariance matrix of the random effects is not positive definite.
For example, i fit the following model:
ggg <- lme (ST~ -1 + as.factor(endp):Z.sas + as.factor(endp), data=dat2a,
random=~-1 + as.factor(endp) + as.factor(endp):Z.sas|as.factor(trials),
correlation = corSymm(form=~1|as.factor(trials)/as.factor(id)),
weights=varIdent(form=~1|endp))
intervals(ggg, which="var-cov")
when i try to access the variance components using the 'intervals' function
i get the following error message:
"Error in intervals.lme(ggg, which = "var-cov") :
Cannot get confidence intervals on var-cov components: Non-positive definite
approximate variance-covariance"
Is there a way out of this? or better still
Is there another function through which i can access these variance
components other than the intervals function?
Kind regards
Pryseley
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