Dear FSL experts,
For my DTI analysis, I am comparing 3 groups and I am including 3 covariates of no interest (age, sex, head motion, the three groups do not significantly differ regarding age in months, sex or head motion). I would like to do an f test to check if there are significant differences between groups and then do the subsequent t-tests.
My design.mat file looks like this:
/NumWaves 5
/NumPoints 54
/Matrix
1 0 0 96 1 1.32
1 0 0 99 0 1.13
1 0 0 97 0 0.77
1 0 0 101 1 2.12 etc…
The columns represent: Group 1, Group 2, Group 3, Age (in months), Sex, head motion.
I have a few questions regarding this:
1. It is not clear for me if the design.fts for the F test should be:
1 0 0 0 0 0
0 1 0 0 0 0
0 0 1 0 0 0
OR
1 1 1 0 0 0?
2. The subsequent design.con for the t-tests file would be:
1 -1 0 0 0 0
-1 1 0 0 0 0
0 1 -1 0 0 0
0 -1 1 0 0 0
1 0 -1 0 0 0
-1 0 1 0 0 0
Is this correct?
3.Is the following command correct?
randomise -i all_FA_skeletonised.nii.gz -o all_FA_skeletonised_comparison_age_sex_headmotion -d design.mat -t design.con -T -n 500
4. I was wondering if I should add the -D for demean since when I do add this option I have the following warning message: “Warning: tfce has detected a large number of integral steps. This operation may require a great deal of time to complete” and I believe when a simple group comparison (with covariates of no interest) is done this is not necessary (?).
Any help would be appreciated.
Thank you in advance,
Ariadna
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