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Hi Enrica,

By centre do you mean an MRI facility? That is, you have 4 MRI scanners and would like to account from them? If that's the case, then you'll need to change the design:

- EV1: use 1 to code controls and -1 to patients
- EV2: use 1 to code centre 1, 0 to code all others
- EV3: use 1 to code centre 2, 0 to code all others
- EV4: use 1 to code centre 3, 0 to code all others
- EV5: use 1 to code centre 4, 0 to code all others.

The contrasts are then:
C1: [1 0 0 0 0] (this tests if controls > patients)
C2: [-1 0 0 0 0] (this tests if patients > controls)

All the best,

Anderson


2015-01-16 11:10 GMT+00:00 SUBSCRIBE FSL Anonymous <[log in to unmask]>:
Hi,

I would like to compare TBSS maps of 2 groups of individual using centers (n=4) as covariate, an example of my design matrix is below:

/NumWaves 3
/NumPoints 74
/PPheights 1 1
/Matrix

 (control) (patients) (covariate-centre)
1              0                1
1              0                1
1              0                2
1              0                2
1              0                3
1              0                3
1              0                4
1              0                4
0              1                1
0              1                1
0              1                2
0              1                2
0              1                3
0              1                3
0              1                4
0              1                4

an example of my contrast is below:

/NumWaves 3
/NumContrasts 2
/PPheights 1 1
/Matrix
1 -1 0
-1 1 0

Are the design matrix and contrast right?

thank you,
cheers,
enrica