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Or can I just treat them as two separate groups so i don't have to rerun individuals? On Tue, Sep 20, 2011 at 11:36 AM, Leslie Engineering < [log in to unmask]> wrote: > So I am a little confused, then. If i have individual subjects that were > run with two EVs contrasts (1,0) (0,1) (1,1), do I have to go back and rerun > each individual subject with contrasts (1,-1)(-1,1) in order to get group > differences or can I manipulate these in some way? > > On Tue, Sep 20, 2011 at 11:14 AM, Michael Harms <[log in to unmask]>wrote: > >> Group contrasts (and statistics) should be calculated from the >> appropriate copes, not done "post-hoc" by subtracting z-maps. >> >> See >> http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#UnpairedTwoGroupDifference >> which provides a clear example of how to proceed. >> >> cheers, >> -MH >> >> On Tue, 2011-09-20 at 11:07 -0400, Leslie Engineering wrote: >> > does it make a difference if instead I have one group that went >> > through a single paradigm, EV. If EV is made up of two separate >> > stimuli blocks and I want to separate them into EV1 and EV2, can I >> > run a single group average using EV1 and a single group average using >> > EV2 then subtract the z scores for an activation difference between >> > the two stimuli? >> > >> > >> > thanks so much >> > >> > On Tue, Sep 20, 2011 at 10:08 AM, Leslie Engineering >> > <[log in to unmask]> wrote: >> > Hello- >> > >> > >> > I ran two separate simple group average analysis. Both groups >> > underwent the same fmri scan sequence. Instead of rerunning a >> > group analysis and included all subjects from both groups and >> > setting up contrasts for group differences (1,-1)(-1,1), is it >> > statistically sound to simply subtract their zscores? >> > >> > >> > >> > >> > >> > >> > >