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Dear Auer, Just use the contrast -1 1 (which is the same as -1 1 0), and TVB will be considered as nuisance variable and taken into account because you have entered it as nuisance variable in the model (you don’t have to specify this variable in the contrast). Gaël. _____ De : SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] De la part de Auer, Tibor MD. Envoyé : jeudi 24 mai 2007 10:19 À : [log in to unmask] Objet : [SPM] VBM using confoundig covariate Dear SPM-ers, I would like to set up an analysis using VBM. I have two groups (patient vs. control) and use their total brain volume (TBV) as described in different sources. I have entered TVB as a confounding covariate, so I have three columns in design matrix (Patient, Contol, TBV). Which t-contrast should I use to take account for TBV? [-1 1 1] or [-1 1 -1] for testing whether Patients have atrophy? Thankfully, Auer, Tibor M.D. PhD-student University of Pécs, Medical Faculty Department of Neurosurgery Rét u. 2, Pécs, H-7623, Hungary Tel.: +36-20-986-9341 E-mail: <mailto:[log in to unmask]> [log in to unmask]