Dear Kelvin
> We have 30 subjects and 30 controls who are tested with the same fMRI
> paradigm. Individual results are analysed (60 con*.img). To analyse
> the group effect, we performed a two sample t test (subject group and
> control group are different) by selecting first 30 subjects from test
> group (con*.img) and selecting the next 30 subjects from control
> group.
>
> In the group definition, we entered 30 '1' and 30 '2'. After all the
> selections (all none/omit), we entered a contrast 1 -1 to evaluate the
> group effect. Is that true that the contrast is a population inference
> (RFX) rather than a FFX within the 60 subjects we collected? We'd like
> to do a RFX.
This corresponds to a RFX analysis because the only source of error is
provided by the between subject variability in contrasts.
> Another question is: If we have a single batch of subjects who undergo
> a treatment and fMRI were acquired before and after the treatment.
> What kind of test should I do to see if the treatment is effective to
> the group in a whole and to the population (if possible)?
A FFX analysis would tell you whether the treament was effective in
that group and an analysis similar to that above (but using a paired t
test at the second level) would emulate a RFX analysis and allow
generalization to the population from which the subjects were sampled.
I hope this helps - Karl
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