[R] Problems computing 2-way-mixed-model ANOVA

[Rolf Turner]

On 6/11/2008, at 11:13 AM, Lucas Eggert wrote:

> Dear Experts,
>
> I am new to R and unfortunately cannot start with a simply statistical
> analysis:
>
> I manually determined the volume of the right and left hippocampus in
> a group of meditators and in a group of controls. My data-sheet looks
> as follows:
>
>
> observation     subject group   age     gender  hemisphere      volume
> 1       am04    m       25      f       left    3.637
> 2       am04    m       25      f       right   3.713
> 3       ao08    m       47      m       left    3.715
>
	<snip>

> 68      ws01    m       30      m       right   5.258
> 69      zz03    m       35      m       left    4.446
> 70      zz03    m       35      m       4.446   4.627
> My attempt to compute the according statistic was:
>
> aov = aov(volume~(hemisphere*group)+Error(subject/hemisphere)+
> (group),input)
>
> but with this I got the following error message:
>
> In aov(volume ~ (hemisphere * group) + Error(subject/hemisphere) +  :
>    Error() Modell ist singulär
>
> I could not figure out what I did wrong. Furthermore, in the next step
> I would like to use gender and age as additional covariates in the
> model, but I am not sure how to do this either.
>
>   Any help would be very much appreciated!

Look at the last line of your data frame.

	cheers,

		Rolf Turner
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