lme model: Error in MEEM

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?

thanks for your kind help
christoph

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--- Urspr??ngliche Nachricht ---
Von: Douglas Bates <dmbates at gmail.com>
An: Christoph Lehmann <christoph.lehmann at gmx.ch>
Kopie: r-help at stat.math.ethz.ch
Betreff: Re: [R] lme model: Error in MEEM
Datum: Thu, 18 Aug 2005 08:29:52 -0500

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

--
Lust, ein paar Euro nebenbei zu verdienen? Ohne Kosten, ohne Risiko!
Satte Provisionen f??r GMX Partner: http://www.gmx.net/de/go/partner

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