[R] lme question

[Andrew Robinson]

Hi Donglei,

what is your goal in fitting this model?  The statement that you've used is 
creating an overparameterized model, as it fits a random intercept for each 
visit within each subject.  I wonder if you might prefer

testresult <- lme(expr~visit, data=testdata, random=~1|subject)

which will fit a random intercept for each subject?

Andrew


On Monday 22 March 2004 14:29, donghu at itsa.ucsf.edu wrote:
> Hi,
>
> I have a dataset like this,
>
> > testdata
>
> Grouped Data: expr ~ visit | subject
>       expr visit subject
> 1 6.502782    V1       A
> 2 6.354506    V1       B
> 3 6.349184    V1       C
> 4 6.386301    V2       A
> 5 6.376405    V2       B
> 6 6.758640    V2       C
> 7 6.414142    V3       A
> 8 6.354521    V3       B
> 9 6.396636    V3       C
>
> I tried the command
>
> > testresult=lme(expr~visit,data=testdata,random=~visit|subject)
>
> I got the following error message.
> Error in MEestimate(lmeSt, grps) : Singularity in backsolve at level 0,
> block 1 In addition: There were 50 or more warnings (use warnings() to see
> the first 50)
>
> Could someone give me some hint on what went wrong?  Thanks.
>
> Donglei Hu
>
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