Reply-To: | | [log in to unmask][log in to unmask]>wrote:
> On Wed, Jan 9, 2013 at 9:08 PM, Jun Wang <[log in to unmask]> wrote: > > Dear spm experts, > > I have a question regarding to post hoc t test in spm. I have a 2X3 > (group > > by task ) repeated design and got significant interaction when I used > > contrast [0 0 0 0 0 1 0 -1 -1 0 1]. > > >>>> The correct interaction contrast is an F-test. [0 0 0 0 0 1 -1 0 -1 0 > 0; 0 0 0 0 0 0 1 -1 0 -1 1]. This will tell you if there is an interaction > between the task effects and group. From this, you could test for pairwise > task difference interacting with your groups. With the post-hoc t-test of > [0 0 0 0 0 1 0 -1 -1 0 1], you know the direction of the effect and don't > need any further tests. > > > Then I want to do post hoc t test to > > tell the direction of interaction( e.g. group difference on task1). > Should I > > extract ROI activity from significant cluster found in the interaction > > effect and do the simple t test outside spm or should I set different > > contrast in same SPM design. if it is the latter case, how should I set > the > > contrast. > > >>>> Testing the group effect of a single task in a repeated-measures > design is not valid with the standard GLM. You'll need a 2-sample t-test. > If you use GLM Flex, then you can test the group effect of individual tasks. > > > > > thanks for your input > > > > Jun >[log in to unmask] |