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You'd still need the F-contrast even in that case. Post-hoc tests would be the same as I stated. There are some things in the Glascher document that should be updated. It's been on my list for quite some time, but never at the top of the list. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Postdoctoral Research Fellow, GRECC, Bedford VA Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Wed, Jan 9, 2013 at 9:46 PM, Jun Wang <[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 > >