Hello all FSL statisticians:
I am working with FSLVBM and would like to create a mixed model to run
in randomise. I have two groups of subjects (sick and not sick) that each
undergo two sessions (pre and post treatment). Does this look like the
correct design and contrast files for this type of analysis? ( have cut the
number of subjects down in each group for ease in viewing...)
Grp EV1 EV2 EV3 EV4 EV5 EV6 EV7 EV8
1 1 1 1 1 0 0 0 0
1 1 1 1 0 1 0 0 0
1 1 1 1 0 0 1 0 0
2 1 -1 -1 0 0 0 1 0
2 1 -1 -1 0 0 0 0 1
1 -1 1 -1 1 0 0 0 0
1 -1 1 -1 0 1 0 0 0
1 -1 1 -1 0 0 1 0 0
2 -1 -1 1 0 0 0 1 0
2 -1 -1 1 0 0 0 0 1
1 2 3 4 5 6 7 8
C1 1 0 0 0 0 0 0 0
C2 0 1 0 0 0 0 0 0
C3 0 0 1 0 0 0 0 0
Because I get an error when I view the design and the Efficiency in the Glm gui:
Problem with processing the model: Warning: at least one EV is (close to) a
linear combination of the others. You probably need to alter your design.
(Design matrix is rank deficient- ratio of min:max eigenvalues in SVD of
matrix is 2.30159e-17)
Warning: design matrix uses different groups (for different variances), but
these do not contain "separable" EVs for the different groups (it is
necessary that, for each EV, only one of the groups has non-zero values)
Also, do you recommend then completing an F-test for main effect? If so, how
do I put that in my contrast file?
Thanks so much for your help!
Cheers,
Kelly Brown
UCHSC Research Fellow
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