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Dear SPM-ers, I have some very basic questions, but I would appreciate if someone could answer... I have SPECT images of a group of Parkinson patients before and after the therapy; and images of control persons... In order to compare the brain activity of controls and that of patients, I do two-sample-ttest. As the first group I enter the controls, and as the second group I enter the corresponding patients. How should I define contrast in order to see where the controls' activity is greater than patients' activity? (1 -1)? In order to compare the brain activity of patients before and afer the therapy, I do paired-ttest. I enter pairs in a sequence: before the therapy, after the therapy... How should I define contrast in order to see where the patients' activity increased during the therapy (-1 1)? Thank you in advance. Petra Tomse -- Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen! Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer