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Dear Will and the other SPM Experts, Following the thread in the SPM-Archive forum by Will Penny, the advices regarding how to set an analysis to investigate both within-subject effects (condition) and between-subject effects (group) we wanted to ask you for a confirmation if we understood the issues discussed correctly so that our design is fit for our planned analyses. Our data: 2 groups: A and B (A=25 subjects, B=21 subjects). 3 conditions: ctrl, con1, con2. We are interested to investigate both the effects of within- and between- subjects effects. In the first level analysis we made the following differential contrasts: d1=con1-ctrl and d2=con2-ctrl for each subject. To our understanding, this can solve the problem of accounting the within-subjects variability and so we can avoid creating a flexible-factorial design in order to investigate the within-subject effects (by including the factor subjects) in the model. Instead (we hope it is correct), we now can set a 2x2 full factorial design and only with 2 factors: group (with 2 levels: A,B) and condition (with 2 levels: d1,d2). This way we can construct contrasts to investigate the effect of condition (within-subject effects) but we can also construct contrasts to investigate the effect of group (between-subject effects) in the same model. Please let us know if we understood the issue correctly or we need to modify any part of our planned design. Thank you very much in advance, Alec & Gil