Re: [R] fix variance parameter values for lmer estimation

From: Douglas Bates <bates_at_stat.wisc.edu>
Date: Fri, 25 Apr 2008 12:06:40 -0500

On 4/25/08, Wilfried Cools <Wilfried.Cools_at_ped.kuleuven.be> wrote:
> Dear list-members,

> a model is fit with lmer, but I want to force the variance parameter values
> to be as defined by me

> I thought, use 'start' to specify initial values and only allow for one
> iteration ?
> my question is how to do that ?

> to specify the 2x2 matrix of variance parameter values:
> start=list(groups=array(2,-0.5,1),dim=c(2,2))

Well, the problem is that if you are going to decide what the arguments to the function should be and how they should be interpreted you are going to need to write the function yourself. There is nothing in the lmer documentation that says it will fit a model with the variance parameter values as defined by you and there is nothing to say that you can specify a list with arbitrary names as the value of the start parameter and somehow lmer will magically infer what you mean by these starting values and do the right thing. Sorry but I don't write mind-reading software. You are going to have to write it yourself.

> now I need to make sure the mean structure is estimated, while the variance
> parameter values are kept constant ??
> e.g. lmer(resp~pred1+pred2+(1 +
> pred1|groups),start=list(groups=array(2,-0.5,1),dim=c(2,2)),....)
>
>
> cheers,
>
>
> Wilfried
>
>
>
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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 25 Apr 2008 - 17:10:20 GMT

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