That matrix will test for an effect of group regressing out the effect of age. I would first test for an interaction between group and age with 0 0 0 1 -1 0 0 0 0 1 0 -1 Assuming that there is no effect, then I would re-run with DOSS (different-offset, same-slope) with a contrast like 1 -1 0 0 1 0 -1 0
DOSS forces all the age slopes to be the same which makes differences in the group intercepts more interpretable
On 12/10/18 1:53 PM, Barletta, Valeria wrote:
Dear Freesurfers,
I am trying to run a GLM analysis with 3 groups (1)long disease duration MS, 2)short disease duration MS, 3)healthy controls) and 1 variable (age).
According to the formula provided on freewiki:
N classes (N of variables + 1),
is this contrast matrix correct?
1 -1 0 0 0 0
1 0 -1 0 0 0
thank you,
Valeria
________________________________ From: Barletta, Valeria Sent: Friday, December 7, 2018 2:23:10 PM To: freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu Subject: glm analysis
Dear Freesurfers,
I am trying to run a GLM analysis with 3 groups (1)long disease duration MS, 2)short disease duration MS, 3)healthy controls) and 1 variable (age).
According to the formula provided on freewiki:
N classes (N of variables + 1),
is this contrast matrix correct?
1 -1 0 0 0 0
1 0 -1 0 0 0
thank you,
Valeria
_______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edumailto:Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer