Hello Friends and Colleagues,
I'm hoping someone might be able to advise about the global scaling
feature of SPM99. I'm looking at comparing the activation elicited by a
cognitive task between a clinical and a nonclinical group of study
participants. I've set up the design to subtract the baseline task from
the "activation" task, etc., and I am clear on how to perform the
subsequent analyses.
One task my advisor has suggested is to compare the baseline conditions to
examine whether or not activation in the more "restful" conditions differ
between the two groups of participants, and to determine if any particular
areas of the brain are more active in one group than in the other when the
brains are at relative "rest". It just occurred to me that perhaps by
using the global scaling and modeling the baseline condition explicitly
(instead of implicitly as SPM99 can do for you) any comparison I perform
between the two sets of baselines could be uninformative, since I've
globally scaled them in order to do the first analysis. (task A - task B)
So my question is, would it be advisable to conduct a new analysis that
includes only the scans for the baseline but this time to avoid using the
global scaling? Intuitively this seems right (to me!), but I'm really not
sure if it is the most appropriate method.
Advise would be greatly appreciated, (and thanks in advance!)
Kristine
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Kristine Boksman, B.Math The University of Western Ontario
M.A.2 Clinical Psychology London, Ontario, CANADA
There are two ways to live your life.
One is as though nothing is a miracle.
The other is as though everything is a miracle.
Albert Einstein (1879-1955)
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