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Dear Rali, The F-contrast you'd like to use uses the 1st and the 5th of your t-contrasts, right? So, the design.fts file that specifies this F-contrast would be: /NumWaves 6 /NumContrasts 1 /Matrix 1 0 0 0 1 0 Each F-contrast (here there is just one) uses one or more of the t-contrasts, coding those that are used as 1, and those that are not used as 0. Note that in this example are exactly 6 columns, which matches the 6 rows of the t-contrast file. Each column corresponds to a row, and the 0 or 1 indicates which should be included in each of the F-tests. Hope this helps! All the best, Anderson 2012/11/27 Rali Dimitrova <[log in to unmask]> > Dear all, > > Just a quick question about setting a f contrast for 3 group comparison in > randomise. I apologize as I have seen similar questions been asked before > but none of them answered my specific question. > > I set the following design.con to look at all possible two-way differences. > /Controls Relatives Patients > /Matrix > 1 -1 0 > -1 1 0 > 1 0 -1 > -1 0 1 > 0 1 -1 > 0 -1 1 > > When I tried to set a f contrast > > /Matrix > 1 -1 0 > 0 1 -1 > > I received the following error message: > 'ERROR: Program failed > An exception has been thrown number of columns in f-contrast matrix > doesn't match number of rows in t-contrast matrix!' > > When I included only three contrasts in the design.con (a priori > hypothesis C>relatives>ill) using the same fts file, randomise ran just > fine. Assuming that the f contrast uses the original EVs from the design > matrix rather than the set contrasts by the design.con, I am not very sure > why I received this message. > > Thank you in advance. > > Best wishes > Rali >