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Hi, Unfortunately your groups are perfectly correlated by center membership and you cannot tease apart group and scanner differences (your design is rank deficient since your first and third regressors are exactly the same as are your 2nd and 4th). This would only be possible if, within a group, you had subjects scanned on both scanners. Although you can compare the groups using a 2-sample t-test there is no way to know whether the difference is due to scanner or group membership. Cheers, Jeanette On Wed, May 16, 2012 at 12:07 PM, Lorena Jimenez-Castro <[log in to unmask]>wrote: > Hello FSL users and experts, > > I want to do a group comparison of resting-state fMRI data, my concert is > that the control subjects (n=25) were scanned in our research center using > a 3 Tesla Siemens Trio scanner . While the patients subjects (n=25) were > scanned in a different center using an identical scanner 3 Tesla Siemens > Trio scanner. > > > Questions: > 1) So, is it possible to do the group comparison? > > 2) If so, Even both scanners are 3 Tesla Siemens Trio scanner, Do I need > to model in the design an EV to remove the effect of scanner/center? > > > if I need to model that, Could be the following design correct? > > > GP EV1 EV2 EV3 EV4 > 1 1 0 1 0 > 1 1 0 1 0 > 1 1 0 1 0 > 2 0 1 0 1 > 2 0 1 0 1 > 2 0 1 0 1 > > EV1 for group 1(controls) > EV2 for group 2 (patients) > EV3 coming from center 1 > EV4 coming from center 2 > > Contrats: > 1. 1 -1 0 0 = control> patients > 2. -1 1 0 0 = patients > controls > 3. 1 0 0 0 = controls mean > 4. 0 1 0 0 = patients mean > > Thank you very much > > Lorena Jimenez Castro, MD >