I have four groups and two covariables. The groups are MCI_P,MCI_S,MCI_R,NC and the covariables are age and education. I want to test the thickness differences of the groups regressing out  age and education.My group.effect.mtx is as following with the feedback of error.

1 -1 0 0 0 0 0 0 0 0 0 0 

1 0 -1 0 0 0 0 0 0 0 0 0

1 0 0 -1 0 0 0 0 0 0 0 0

       Thanks! I am looking forward for your prompt reply.

                    Yours,

                     Haidong