Dear SPM experts,
Iīm sorry to come back to this issue again but depite all postings regarding
this topic I still have problems to understand and how to do it.
Iīm using the VBM5.1 toolbox and I want to compare GM volume between 2
groups using total GM volume as covariate of no interest. So I performed an
ANCOVA (Full factorial design, Ancova=Yes under Factor section, defining the
covariate under Covariate section). Now I want to extract the raw data for
each subject at a specific coordinate and want to feed them into SPSS. I
tried using the button eigenvariate, VOIradius = 0 mm, typing Y in matlab.
As far as I know the voxel value is the probability of that voxel being grey
matter. But this is confusing me since I want to see whether the voxel
values of the subjects of one group are increased or decreased compared to
the voxel values of the subjects of the other group. But probabilities
donīt tell me that (?). I also donīt understand how I can do calculations
with these values, e.g. with the total GM volume (I assume the raw data are
not corrected for total GM volume), since I have then probabilities (voxel
value) and ml (total GM volume).
I would be really grateful if anybody could help me with this problem.
Thank you very much in advance!