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Dear Anderson and Experts, I would like to follow up on Maya's question and ask if looking at t-contrast she presented in the second model e.g [1 1 -1 -1] would be a valid thing to do. I'm working on a similar statistical model in TBSS (2x2 ANOVA) and I also find main and interaction F-contrasts empty. The F-contrasts are modelled the way it was recommended on GLM webpage (ANOVA: 2 factors 2 levels). Some directional t-tests in two main contrasts and interaction e.g. A>B contain significant results surviving FWE correction. The differences stand when the two-group model is created and the two groups compared, so EV1=A and EV2=B. When all 4 groups (Ax, Ay, Bx, By) are put together in one F-contrast the way described on GLM webpage (ANOVA: 1 factor 4 levels) they also give significant results surviving FWE correction, this time in F-contrast. The empty F-contrasts appear only when two groups are compared in them like A vs B or x vs y. It stays the same with both 500 and 5000 permutations and two different versions of FSL. My questions are: a) is it valid in ANOVA in FSL to look at two directional t-contrasts e.g [1 1 -1 -1] and [-1 -1 1 1] instead of F-contrast. I've seen some papers doing this. It is also valid in SPM. Is FSL coded in such a way that it is valid? b) why would the F-contrasts like A vs B, x vs y, AB interaction xy give no results yet F-contrast of Ax, Ay, Bx, By and t-contrasts of A vs B, x vs y, AB interaction xy would be highly significant? All the best, Danusia