Dear Sarah,
> I am using optimized vbm (spm2) to compare two clinical groups (A & B) and one control group (C) and thresholded all results at
> p<0.001 uncorrected.
>
> I would like to find all voxels that are equal in the contrasts C>A and C>B. Would it be a valid approach
> to use a conjunction analysis with C>A Ç C>B? Could it be a problem that the group C occurs in both contrasts?
what you would like to do, is that what Tom Nichols is describing in his 2005 Paper about valid conjunctions, which also works, if the contrast are not independent.
See also: http://www.sph.umich.edu/~nichols/Conj/
Good luck,
Karsten
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Karsten Specht, PhD
Department of Biological and Medical Psychology
& National Competence Centre for functional MRI
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
[log in to unmask]
http://fmri.uib.no/
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