Hi! I'm wanting to contrast two groups and am confused about how to ask my
question. Sorry if it's a bit basic, i'm sure some of you will groan to see
it come up. I'm trying to interpret this typical contrast:
CONTROLS (task > baseline) > PATIENTS (task > baseline)
i.e., (A>B) > (C>D)
i.e., (1-1) - (1-1)
I've been told that if I run the contrast (A>B) > (C>D) and EXCLUDE any
areas activated in (D>C), I can safely interpret my results as being areas
that are more active in controls than patients (for task>baseline).
The exclusive mask is apparently because the above contrast is the same as
(D>C) > (B>A)
I.e., a brain region more active in task during controls could also be a
region that is more active in baseline in patients.
I just wanted to check – is an exclusive mask the correct way to resolve
this? I’m worried there could be some regions that are active in BOTH
(A>B) > (C>D) and in
(D>C).
I.e., some brain regions could be more active in task in controls, and
simultaneously less active in task in patients. Am I wrong? If I’m
correct, what’s the best thing to do here? Inclusively mask with A>B? Or
do we just have to live with the ambiguity?
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