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Hi, all£¬ I am doing a VBM study to compare a patients group and a control group by SPM2. I have used VBM scripts from Christian Gasers (http://dbm.neuro.uni-jena.de/vbm.html) and generated the optimized segemented gray matter files. If i want to compare the GMV (gray matter volume), i should use the mGwxxx files (modulated file), but if i want to compare GMC (gray matter concentration/density), i should use Gwxxx (non-modulated) files directly, right? And, i am using the PET model to do the statistics (Compare-populations: 1scan/subject, AnCova). I used the following parameters: two groups (24 controls vs. 25 patients), two nuisance variables(age, gender), no global normalisation, no grand mean scaling, absolute masking(threshold = 0.1), omit global calculation, yes for non-sphericity correction, relications over subject(25), yes for correlated repeated measures. Are these parameters right? What are the meaning of relications over subject(25) or over group (2), and the meaning of correlated repeated measures? Thanka a lot for any suggestions. best,¡¡¡¡ ---------------------------- Hengyi Rao, Ph.D. [log in to unmask] Department of Neurology University of Pennsylvania 3 W Gates 3400 Spruce Street Philadelphia, PA, 19104 ----------------------------