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Dear FSL experts, I am running a TBSS analysis on a group of healthy subjects. I have their FA images, along with their age, sex, and anxiety scale. Age and sex are covariate of no interest, and I want to check if the anxiety scale has a correlation with FA. My design.mat file is something like this /NumWaves 4 /NumPoints 21 /PPheights 1 1 /Matrix 1 -16,1428571428571 2,74238095238096 -0,333333333333333 1 -13,1428571428571 1,99238095238096 -0,333333333333333 1 -11,1428571428571 3,84238095238096 -0,333333333333333 1 40,8571428571429 -1,40761904761904 -0,333333333333333 ... where the first column is the group (1=healthy subjects, they are 21), the second column is the demeaned anxiety scale, the third column is the demeaned age, and the fourth column is the demeaned sex. My problem is in the definition of NumWaves in the design.con file. Is it correct to write it like this? And what about the NumContrasts? /NumWaves 4 /NumContrasts 3 /PPheights 1 1 /Matrix 1 0 0 -1 0 0 Thank you in advance, elisa