On Thu, 31 Mar 2005, Thomas E. Nichols wrote:
<snip>
> If you would like to conclude that the effects corresponding to
> all three of these contrasts are simeltaneously "real", then you
> want to use the "Conj'" null.
>
<snip>
> For more, see http://www.sph.umich.edu/~nichols/Conj and the
> two articles on Conjunctions on the "In Press" section of
> NeuroImage website.
Tom,
Thanks again for your previous reply. I have taken a look at your
paper and installed your patches to SPM 99. I assume the patches change
the meaning of "conjunction" in the spm gui so that conjunction is now
MS/CN from you paper and "global" is now MS/GN. I understood from your
paper that the correct conjoined region is found by taking the
intersection of all voxels which tested significant in the individual
tests (eg performing a voxel-wise logical AND).
If that is the case, I should be able to get the same region by
running the tests individually and finding the intersection os those
regions. Using the marsbar package, I was able to do precisely that for
the FWE correction, but not when I used the FDR corrections. Is it invalid
to use FDR corrections with conjunction?
thanks again for the advice!
bjorn
|