to do the between-groups analysis, use the two-sample t-test option under
basic models and then provide the subject-specific con*.img files for each
of your two groups. this will test for differences in that effect between
the groups (in either direction depending upon the contrast you specify).
cheers
russ
Henrik Walter wrote:
> Dear SPMlers,
>
> supposse the following study:
> Group A: 12 patients
> Group B: 12 controls.
> Each groups performs Task I and II.
>
> We are interested in task specific effects withingroups and group
> differences between tasks.
>
> To analyse within group effects I perform two fixed effects analysis,
> for each group seperately with 12 subjects, compute subjects specific
> con-images and feed them into a second level, Rx-analysis. So far so
> clear.
>
> But what if I want to know something about the group differences for
> Task A? I see two possibilities: Either I take the con-images of each
> group specific Fx-effects analysis. OR I do a third Fx-Effects analysis
> with all 24 subjects in one group. The main difference is that global
> normalisation in the first case is group specific in the second case
> not. But isnt the second case, i.e. to make a new Fx-effects analysis
> not the correct way because I want to compare both groups?
>
> Thanks for an advice
>
> H. Walter
>
> --
> Dr. Dr. Henrik Walter
> Abteilung Psychiatrie III
> Universitätsklinikum Ulm
> Leimgrubenweg 12
> 89075 Ulm
>
> fon: 0731/502 1489
> fax: 0731/502 1549
> e-mail: [log in to unmask]
--
Russell A. Poldrack, Ph. D.
Assistant Professor of Radiology, Harvard Medical School
MGH-NMR Center
Building 149, 13th St.
Charlestown, MA 02129
Phone: 617-726-4060
FAX: 617-726-7422
Email: [log in to unmask]
Web Page: http://www.nmr.mgh.harvard.edu/~poldrack
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