Dear FSL experts,

when performing a dual regression analysis of my data, I encountered a problem with the design matrix. I'm investigating the differences in resting state of 2 groups, while correcting for several covariates (e.g. motion parameter, brain volume, age,...).

I arranged it as described below (or have a look at the attachment):

EV1   EV2   EV3   EV4....
1       0        2       1
1       0       -1       -3
1       0       -3       5
1       0       4        2
1       0       5        4
0       1       -2       -1
0       1       3        -2
0       1       -4       -5
0       1       1         -4
0       1       -5        3

EV1 codes for Group1 and EV2 for Group 2, while EV3 and EV4 are some covariates (demeaned). After doing melodic, I ran:

dual_regression /somewhere/melodic_IC 1 -1 0 /somewhere/output `cat /somewhere/something.txt`

Subsequently, I ran randomise with the components of potential interest.

Now, I used the attached design.mat and design.con files and got my tfce_corrp_tstat images, indicating the group differences. Till now, everything was fine.

However, when adjusting my .mat and .con files (e.g. deleting age from the covariate list..thus no longer correcting for age effects), I noticed, that the resulting tfce_corrp_tstat outputs were absolutely identical!

I repeated this for several combinations of covariates, and even without putting any covariate into the analysis, but still all the outputs were identical. I have no clue on what is going wrong, but there seems to be a problem in how I am processing my data.


PS: I also tried to define 2 groups in a design.grp file withe 2 columns for each EV, but this also ended up with the identical output images.