Dear Freesurfer experts,

 

I am modelling multiple covariates (age, SES, nr of symptoms and nr of
symptoms2) in one subject group. For the quadratic term I added a column in
the fsgd-file. I want to visualize the effect of nr of symptoms, either
their linear or their quadratic effects. I therefore made two contrasts:

 

The effect of symptoms: 

 

0 0 1 0

 

And the effect of symptoms2:

 

0 0 0 1

 

I would like to model these two effects together in one contrast (to get the
results of both contrasts overlaid on top of each other, but in one mgh
file). I tried the following contrast:

 

0 0 1 0

0 0 0 1

 

But the result is very different from the two individual contrasts. I get
large (non-overlapping) clusters of significant effect in the two separate
contrasts, but with the combined contrasts I get none.  In the examples I
found online for F-contrasts, they always add up to zero, as they are
comparisons between groups. What would be the appropriate contrast if I want
to visualize all regions with EITHER a linear OR a quadratic effect of
symptoms?

 

Thank you very much for your help!

 

Best wishes, Lizanne

 

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