Dear Donald and SPM-experts,
I have two questions regarding the GLM flex:
- To get used to the tool I compared the results of a 2x2 flexible
factorial (+ the subject factor since the second one is within-subject
factor) in SPM8 with the results from the GLM flex. Interestingly, the
result from GLM flex is very different from the standard SPM8 analysis
AND similarly different from the SPM computation which was created by
GLM flex (ComptOpt=1). I was wondering why this differs from the latter
analysis since only the final contrast is created "manually" in SPM8. I
understand that the standard SPM analysis is slightly different from the
SPM computation by GLM flex due to modeling of the error terms.
- Now I would like to include a third factor (also 2 levels) and run a
3-way interaction (which if I understood correctly is not possible in SPM8).
The problem is that the factor matrix now has 5 columns (although the
first and last columns are identical) which gives an error. Leaving out
the SPM computation avoids this error, but I am not sure how to set the
contrast for the interaction (see attached design matrix):
-- the first gives an empty file:
I.Cons(1).c = [zeros(1,6)] 1 -1 -1 1 -1 1 1 -1 zeros(1,31)]
-- the second would give a result - but then I am still stuck with the
very first problem that GLM flex was different from the SPM analysis:
I.Cons(1).Groups = {7 8 9 10 11 12 13 14}
I.Cons(1).Levs = [2 2 2]
Thank you for your help and best regards,
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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