Dear FreeSurfer experts,

I have two binary factors (F1: F1L1 F1L2; F2: F2L1 F2L2), 1 covariate (COV), and 1 nuisance factor (NUI). I want to make sense of some specification of the regressors and contrasts.

Because they are not described in http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G1V, I post my understanding below. Can you let me know if it is correct?

This model using the DODS method will have 12 regressors:

Regressor1: 1's for F1L1 F2L1, 0 otherwise (i.e., offset for Group 1)

Regressor2: 1's for F1L1 F2L2, 0 otherwise (i.e, offset for Group 2)

Regressor3: 1's for F1L2 F2L1, 0 otherwise (i.e., offset for Group 3) 

Regressor4: 1's for F1L2 F2L2, 0 otherwise (i.e., offset for Group 4)

Regressor5: COV for Group1 subjects, 0 otherwise (i.e., COV slope for Group 1)

Regressor6: COV for Group2 subjects, 0 otherwise (i.e., COV slope for Group 2)

Regressor7: COV for Group3 subjects, 0 otherwise (i.e., COV slope for Group 3)

Regressor8: COV for Group4 subjects, 0 otherwise (i.e., COV slope for Group 4)

Description1: Does the correlation between thickness and COV, accounting for F1 and F2, differ from 0? Nuisance factors: NUI

Contrast1: [0  0  0  0  0.25  0.25  0.25  0.25  0  0  0  0]

Best,

Daniel