We conducted a PET study to look at the effects of drug prior to and
following surgery. Each patient had 15 scans before surgery and 15 scans
after surgery. The first 5 scans are baseline, that is, no drug was
administered ("off" scans). Following, the first 5 scans, the drug was
injected and we have a variable number of "on" scans for each patient. To
look at the differences between the "on" and "off scans the following was
done:
In SPM95, we entered the following commands:
Statsitics
select design type? Multisubject with replications
# of subjects? 7
# of conditions? 2
selected "on" scans for condition 1 and "off" scans for condition
2 for each subject
select global normalization? proportional scaling
image left = subject left
gray matter threshold? 0.8
grand mean? 50
# contrasts? 1
[2]-contrast 1: 1 -1
Is this correct for our contrast of interest? How does SPM95 deal with the
variable number of scans for each subject? Does it take the average of the
on scans and the average of the off scans for each subject?
Thank you for your assistance.
Jennifer
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