lme$apVar and PROC MIXED Std. Error of varcomp ests

[Sven.Knudsen@adeptscience.dk]

Dear S group

I am currently evaluating the S-PLUS lme
fucntion. The output I try to recreate is from PROC MIXED (SAS version
6.1). As far as I can understand, the two procedures base standard errors
of variance components on minus the invers of the Hessian matrix; at lesat
that is what the intervals method for lme object does. However, the std.
erros differ from the SAS out put when extracted from an lme object via
sqrt(diag(lme.obj$apVar)). Am I doing something wrong here?  

Few years ago, I heard a roumer that SAS
did compute these values with error - is this what I am discovering here
with SAS version 6.1?

Adept Scientific ApS

Sven Jesper Knudsen
Senior Consultant