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

[David Winsemius]

On 11/19/19 8:59 AM, bill using denney.ws wrote:
> Hi Bert,
>
>   
>
> If the statistical reason is off topic here, do you have a suggestion of a better forum?

There are two forums of the top of my head. The first should have been 
obvious if you had reviewed the mailing lists under the r-project.org 
domain, i.e. the mixed effects SIG list. The other would be 
CrossValidated.com


-- 

David.

>
>   
>
> Thanks,
>
>   
>
> Bill
>
>   
>
> From: Bert Gunter <bgunter.4567 using gmail.com>
> Sent: Tuesday, November 19, 2019 11:52 AM
> To: bill using denney.ws
> Cc: R-help <r-help using r-project.org>
> Subject: Re: [R] Why does nlme::getVarCov not Work for nlme Models?
>
>   
>
> 1. The Help page for getVarCov says that it supports lme and gls models only. So not nonlinear models. As to why it does not, that is off topic here, as that is a statistical question.
>
>   
>
> 2. As this is longstanding, it almost certainly has good reason for being there, so I would seriously doubt it. But of course I don't speak for R Core.
>
>   
>
> Cheers,
>
> Bert
>
>   
>
> On Mon, Nov 18, 2019 at 9:43 PM <bill using denney.ws <mailto:bill using denney.ws> > wrote:
>
> 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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>
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