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Dear FSL people, I use FSL on a windows XP. I have 24 subjects and each subject did 3 sessions. The sessions are the same experiment (basically, I had each subject do the experiment 3 times to get better power/enough trials). I have succesfully performed a first level analysis for each session separately (so 72 separate analyses). I would now like to make the leap to higher level analyses. As far as I know, I should first do a second level analysis for each subject over the 3 sessions (to get the mean effect for each subject) and then finally a third level analysis over the 24 subjects (to get the mean effect for all subjects). I run into trouble when trying to do the second level analysis. According to the manual, 'putting all the subjects into one second level analysis should make the estimation of cross-session variance more robust'. However, In my case this leads to a second level analysis with 72 'inputs' (the rows when specifying the GLM) and 24 EV's. Unfortunately, FSL does not seem to be able to cope with this amount (my FSL basically freezes when I try to specify so many EV's). I suppose I don't quite understand why putting all the subjects into 1 second level analysis (as opposed to for example doing 24 separate second level analyses) would be better, since you're not taking between subject variances into account yet. So basically, here's my question: Would I loose statistical power when I decided to instead split this second level analysis up? My idea is to first do the first 12 subjects (so 36 'inputs' and 12 EV's) and then the second 12 subjects. Is there a problem with doing the second level analysis this way, seeing as I should still wind up with 24 copes for the third level analysis... To be honest, I don't see any other way for me to analyze my dataset. Merry Christmas, Bianca.