[R] Error() model is singular - what does that mean

[peter dalgaard]

On Jul 2, 2012, at 20:02 , zetwal wrote:

> On changing the parameters; using only Error(User), I don't get any warning
> on singularity. However most tutorials I saw seemed to point to using
> Error(User/(whatever i specified before))
> 
> Are there some rules which indicated when I should use only Error(User) and
> Error(User/(...))

Not really, but if you don't have a completely balanced User*A*B design, then aov() likely gets in trouble. 

If I understand your original message correctly, you have 9 observations per subject but 5 levels of the within-subject factors, so that with N subjects you have 9N observations but the error model tries to fit 25N parameters and this is what triggers the error message. With just the Error(User) term, the model has just N parameters and things are fine, although I suppose you get the A*B effects tested in both strata. 

> 
> Thanks
> Pascal
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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