As the original post suggested, age is collinear with the subject
columns, so your not explaining any more variance. Depending on your
question, you have two options:
(1) Create the linear effect of the three levels and then use a
one-sample t-test with a covariate;
(2) Use a program other than SPM that can properly handle
repeated-measure ANCOVAs. A small warning, different programs will
give you different results as each program does the analysis slightly
differently. Also, this is no longer in the GLM framework, which is
why its not done in SPM. I believe AFNI has a new tool for linear
mixed models.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Thu, Oct 25, 2012 at 6:03 AM, Andreas Hahn
<[log in to unmask]> wrote:
> Dear SPM-experts,
>
> I am currently facing a problem which has been posted to the list but I can
> not find a solution:
> https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0808&L=SPM&P=R7442&I=-3&d=No+Match%3BMatch%3BMatches
>
> I would like to enter age as a covariate of no interest in a repeated
> measures ANOVA design (20 subjects, 1 condition with 3 levels). The question
> is how to construct the covariate vector? Since the scans are carried out
> within a rather short duration, age does not change between the scans.
> However, entering the same age for each of the 3 scans for each subject
> gives the identical result as without the covariate.
>
> Thank you for your help in advance,
> Andreas.
>
> --
> Andreas Hahn, MSc.
> Functional, Molecular & Translational Neuroimaging
> Department of Psychiatry and Psychotherapy
> Medical University of Vienna, Austria
> Phone: +43 664 8001662002
> Email: [log in to unmask]
> Web: http://www.meduniwien.ac.at/neuroimaging/
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