Both of those contrasts will give you the same p-value. The difference is if you look at the contrast values themselves (gamma.nii). The first contrast will give you values in units of mm. The second will give you values in units of 4*mm.
doug
Per Selnes wrote:
I'm trying to set ut a freesurfer group analysis. In my fsgd file there are four groups/classes and 2 variables, like so:
GroupDescriptorFile 1 Title Class Class1 Class Class2 Class Class3 Class Class4 SomeTag
Variables Variable1 Variable2 Input subj1 Class1 49 1 Input subj2 Class2 50 2 Input subj3 Class3 51 3 Input subj3 Class4 52 4 Input...
I'm a bit puzzled as to how I should set up the contrasts. With DODS, there should be a matrix of 12 regressors, and I want to model how thickness varies with Variable2, ignoring the effects of Variable1 and Class. Should my contrast be
0 0 0 0 0 0 0 0 0.25 0.25 0.25 0.25 or 0 0 0 0 0 0 0 0 1 1 1 1
or something completely different?
I have tried both contrasts, and they yield identical (and plausible) results.
Kind Regards, Per Selnes _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer