Hi FSl users
I have run a VBM analysis with one group of 121 particpants, looking to understand the effect of a behavioural variable. My GLM is set up as
EV1 EV2
Group Score
1 19.1
1 40.9
1 -15.4
etc etc
(note: I have demeaned the behavioural score before entering it in the GLM as my computer seems to stall when using -D in randomise)
My question is: What is the difference between using the contrasts of C1 [1 1], C2 [1 -1] vs C1 [0 1], C2 [0 -1]?
I understand from the fsl website (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/GLM#Single-Group_Average_with_Additional_Covariate) the latter contrasts should give positive and negative correlations of the behavioural score with GM intensity. However, I am confused by what the first contrasts are showing? They produce highly significant findings in regions supported by existing literature.
Thankyou for any help,
Casey
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