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Dear SPMers, I am studying a group of 9 patients and 7 controls. Of the 9 patients, 5 have had bilateral optic neuritis (5 R & 5 L), 4 patients have had unilateral optic neuritis.(2R and 2L); I want to compare the activation in this group with controls. The 5 patients with bilateral optic neuritis, the R eye and L eye contrasts are dependant as they are from the same patient, as are the 7 controls. How do I include the 4 patients who have had unilateral involvement, as their affected eyes (2R and 2L) are independent as they are from different patients, in the same model? I do not want to include the 4 unaffected eyes in the patient group. In full factorial, I am allowed to specify the variables as either dependant or independent for each factor. For eg: If factor 1 is subjects, with Patients v Controls (independent) and Factor 2 is eyes, Left v Right, independent for the unilateral involvement and dependent for the bilateral involvement and controls. But I am not able to separately specify the independence for the subgroups. Please can anyone help me get around this problem without having to leave out the unilateral affected eyes, just to fit in the model? Many thanks Madhan Kolappan