Hi all,

I’m performing an FBA analysis and I’m at the statistical analysis step with fixelcfestats. In my analysis, I have two groups to be compared and 3 covariates. I wrote the design matrix as follows (for an example of 6 subjects, 3 for each group):

1 1 -9.63 0 101632.23

1 1 3.37 1 68083.234

1 1 -8.63 1 -33305.765

1 -1 -5.63 0 54037.234

1 -1 -3.63 1 23039.234

1 -1 2.37 0 27409.234

After the intercept the 2nd column is the group, then covariates (age, sex and icv). The contrast file is

0 1 0 0 0

0 0 1 0 0

to respectively test the group effect and the age effect.

However, when I run the fixelcfestats I have the warning of rank-deficient matrix and I can not understand why.

I’m very grateful if you can help me.

Thanks

Sara