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Dear Lucas, for a group comparison, you would have to model a regressor for group. If you have regressors for "group", "IV", "age", "gender" you'd have to set the contrast weight either 1 0 0 0 or -1 0 0 0 for a t-test showing group1 > group2 or group2 > group1 respectively, controlling for IV, age, and gender. Good luck, Udo Lucas Eggert schrieb am 2009-06-27: > Dear Donald McLaren, > >You want [1 0 0] which is the positive effect, assuming a T-test, > >of your IV on volume. > >[1 1 1] is the average effect of your IV, age, and gender. This > >would be very hard to interpret. > Ok. > In case, I would try a two-sample t-test to compare the gray matter > volume between two groups, again controlling for the effect of age > and gender, > would the contrast be defined analogously, i.e. e.g. "1 -1 0 0"? Or > would I do this also in a multiple regression model with an > additional regressor 'group'? And would the > contrast be "1 1 0 0" then (for "group", "IV", "age", "gender")? > Thank you very much for your help! > All the best, > -Lucas -- Dr. med. Dipl.-Psych. Udo Dannlowski Cognitive Neuropsychiatry Research Group Department of Psychiatry University of Münster Albert-Schweitzer-Str. 11 48149 Münster Phone: ++49 251 8356601 Fax : ++49 251 8356612 email: [log in to unmask]