[R] Why does nlme::getVarCov not Work for nlme Models?

[biii m@iii@g oii de@@ey@ws]

Hi,

 

I was just trying to summarize an nlme model using `broom.mixed::tidy()`,
and it doesn't give random effects or residual variability for nlme models.
As I looked deeper, this appears to be related to the fact that
`nlme::getVarCorr()` doesn't support nlme models for no reason that I can
discern [1].  I do see that it simply has a `stop()` call if the model is
nlme, but I don't know or see a commented reason why this would be.

 

I can imagine that in a nonlinear model the interpretation of variance is
different than in a linear model (namely that it is more likely to be
asymmetric and this result is asymptotic), but that doesn't seem like a
reason to prevent the use of the tool.  When I pretended that my model was
an lme model (set the class temporarily to "lme"), it gave the expected
result.

 

My questions are:

 

1.	Why does nlme::getVarCorr() not support nlme models?
2.	If there is not a known reason, does someone in R-core think that a
patch removing the stop below [1] would be accepted?

 

[1] https://svn.r-project.org/R-packages/trunk/nlme/R/VarCov.R the lines
are:

    if(any("nlme" == class(obj)))

        stop("not implemented for \"nlme\" objects")

 

Thanks,

 

Bill


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