Reply-To: | | [log in to unmask][log in to unmask]> wrote: > > Thanks,Donald. If my two factors are all within subject factor(3 time > window > > and 2 task condition), then I can use the contrast [0 0 0 0 0 1 0 -1 -1 > 0 > > 1]. right ( I just followed the example from Glascher's paper). in this > > case, how should I set the contrast for posthoc t test right. basically, > I > > want to know the task difference on different time window > > > > thanks > > Jun > > > > > > On Wed, Jan 9, 2013 at 8:14 PM, MCLAREN, Donald < > [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] |