Dear SPMers,
I would like to include a covariate in a fMRI flexible factorial design with three factors: Subjects (30 subjects) Group (2:experimental and control group) Time (2: pre and post treatment). The SPM manual specifies that the covariate has to be entered per subject (i.e all values for subject 1, all values for subject 2...) so I suposse I should enter the vector as 2x30 vector. However, I only want to covariate by pre-treatment brain volume values because I have found significant differences at baseline and brain volume change after treatment is also an outcome measure that could lead to brain functional reorganization . It could be a possibility to include the basal atrophy values as the values in pre-treatment and post-treatment or I am commiting any methodologycal bias?
Thank you in advance,
Oiane
|