A question: are there two subjects in each group (G1, G2, G3)? Or one subject in each group with two scans?
Demean: (http://mumford.fmripower.org/mean_centering/)
For two subjects case:
G1 G2 G3 CNI_1 CNI_2
1 0 0 -0.667 -9.333
1 0 0 0.333 12.667
0 1 0 0.333 1.667
0 1 0 -0.667 -6.337
0 0 1 0.333 10.667
0 0 1 0.333 -9.333
For one subject case:
You’d better get the average FA map from the two scans. Then use the following design matrix:
G1 G2 G3 CNI_1 CNI_2
1 0 0 -0.167 1.5
0 1 0 -0.167 -3
0 0 1 0.333 1.5
Contrast1: 1 -1 0 0 0
Contrast2: 1 0 -1 0 0
Contrast3: 0 1 -1 0 0
Yingying
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]]
On Behalf Of R Duke
Sent: Wednesday, May 16, 2012 3:13 PM
To: [log in to unmask]
Subject: [FSL] Randomise Contrast
I have a question regarding my Randomise design matrix. I have three groups (G1,
G2, G3) and two covariates of no interest (CNI). I am interested in between group FA differences and feel that I should control for my two covariates of no
interest. Given this information I was wondering if the design matrix I have listed below is correct?
G1
|
G2
|
G3
|
CNI_1_G1
|
CNI_1_G2
|
CNI_1_G3
|
CNI_2_G1
|
CNI_2_G2
|
CNI_2_G3
|
|
1
|
0
|
0
|
1
|
0
|
0
|
22
|
0
|
0
|
|
1
|
0
|
0
|
2
|
0
|
0
|
44
|
0
|
0
|
|
0
|
1
|
0
|
0
|
2
|
0
|
0
|
33
|
0
|
|
0
|
1
|
0
|
0
|
1
|
0
|
0
|
25
|
0
|
|
0
|
0
|
1
|
0
|
0
|
2
|
0
|
0
|
42
|
|
0
|
0
|
1
|
0
|
0
|
2
|
0
|
0
|
22
|
|
Contrast1: 1 -1 0 0 0 0 0 0 (give me voxels where FA for G1 > FA for G2)
Contrast2: 1 0 -1 0 0 0 0 0 0 (give me voxels where FA for G1 > FA for G3)
Contrast3: 0 1 -1 0 0 0 0 0 0 (give me voxels where FA for G2 > FA for G3)
I was also wondering if this design controls for within or between group variance?
In other words, what happens if I put my two covariates of no interest in only 2 columns (just listing the covariate of no interest across each group in two columns -
one column for CNI_1 across all groups and one column for CNI_2 across all groups)? Would this be controlling for between group differences?