[R] lme model: Error in MEEM

[Douglas Bates]

On 8/18/05, Christoph Lehmann <christoph.lehmann at gmx.ch> wrote:
> Hi,
> We have data of two groups of subjects: 32 elderly, 14 young adults. for
> each subject we have 15 observations, each observation consisting of a
> reaction-time measure (RT) and an activation maesure (betadlpcv).
> since we want to analyze the influence of (age-)group and RT on the
> activation, we call:
> 
> lme(betadlpcv ~ RT*group, data=our.data, random=~ RT |subject)
> 
> this yields:
> Error in MEEM(object, conLin, control$niterEM) :
>         Singularity in backsolve at level 0, block 1
> In addition: Warning message:
> Fewer observations than random effects in all level 1 groups in:
> lme.formula(betadlpcv ~ RT * group, data = patrizia.data, random = ~RT |
> 
> what's the problem here?

It seems that you only have one observation per subject and you are
trying to estimate a model with two random effects per subject plus
the per-observation noise term.  These terms are completely
confounded.
> 
> thanks for your kind help
> christoph
> 
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