Hi,
I would like some clarification on what "effects of interest" means when
looking at a single factor correlating with activation within subjects.
Using SPM2 I have a design with one measured factor (e.g. hormone level)
correlated with PET perfusion images within subjects (10 subjects, 12 scans
per subject).
When looking at the SPM2 default F-test results, some regions appear
significant that do not appear when looking at the linear contrasts for
positive correlations ([1 1 1 1 1 ...]) or negative correlations ([-1 -1 -1
...]). Even if you drop the significance thresholds, the linear contrasts
are stuggling to find anything in those areas.
Is this "effect of interest" F-test looking for absolute significant
correlations that are either ALL positive or ALL negative, or is it, in this
case, (a less useful?) test that might find significance where, for example
half of the subjects positively correlate & half negatively correlate?
Or does the "effect of interest" in multisubject/scan correlation mean
something else entirely?
Help appreciated.
Cheers
Joel
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