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Dear Helmut, I guess your contrasts compare a reduced model to the full one, which is probably not what you want. To find out differences between conditions irrespective of their signs I think it's appropriate to specify the contrast- "matrix" for the F-test as if it were a t-contrast, i.e: [-1 1] or [-1 1 -1 1] but still doing an F-test. Please correct me, if I'm wrong.... Thilo On Tuesday 20 September 2005 19:47, Helmut Laufs wrote: > Dear SPMers, > > to test whether there is any difference (i.e. irrespective of the direction > of signal change) between two conditions, is it valid to do an F contrast > like this: > > [-1 0; > 0 1] > > ? > > ..and extending this to two sessions (repeated conditions) in one design > (let's assume, there are only 2 conditions/colums per session): > > [-1 0; > 0 1; > 0 0 -1; > 0 0 0 1] > > ? > > It looked straight forward to me in the first place, but now I am confused. > > Any help appreciated. > > Thank you. > > Helmut -- Thilo Kellermann RWTH Aachen University Pauwelstr. 30 52074 Aachen Tel.: +49 (0)241 / 8089977 Fax.: +49 (0)241 / 8082401 E-Mail: [log in to unmask]