Re: [R] lme: error message with random=~1

[Ramon Diaz-Uriarte]

On Wednesday 05 January 2005 16:29, Thomas Petzoldt wrote:
> Douglas Bates wrote:
> > I'm not sure what model you want to fit here.  To specify a random
> > effect in lme you need both a grouping factor and a model matrix.  The
> > error message indicates that lme is unable to determine a grouping
> > factor.  It would be correct syntax if you added a single level factor
> > to the data frame and used that but then the model fit would fail
> > because you would be trying to estimate a variance in a model where
> > there is no variation in the term.
>
> O.k. I see and think I understand it.
>
> > It seems to me that you are trying to estimate parameters in a
> > mixed-effects model without any random effects and lme can't do that.
>
> Yes, what I want is a model without any random effects to be tested
> against a model with random effects. I want to show, that the random
> effects are negligible but that we account for pseudo replicates and
> have tested this explicitely.

Dear Tomas,

What about fitting the models with and without random effects using the gls 
function (instead of lme ---you'll need to change a bit the syntax in the 
model with random effects in lm), and using a LR test? 

R.
>
> I'm not sure what is better: to leave the random effects in the model or
>   simply an LR test against a linear model fitted by lm. I've never seen
> such an example in the books. Or have I missed a global alternative here?
>
> Thomas P.
>
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-- 
Ramón Díaz-Uriarte
Bioinformatics Unit
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(Spanish National Cancer Center)
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