Dear freesurfers,

for a morphometry study, I am comparing a single subject at a time to a group of controls. I would like to include age, gender (as a continuous variable for the sake of simplicity) and eTIV as “nuisance” regressors in the GLM. The FSGD looks like this:

GroupDescriptorFile 1
   Title SUBJECT1_vs_allControls
   Class Test
   Class Controls
   Variables Age Gender eTIV

Input SUBJECT1 Test 50 1 1497422.2500
Input SUBJECT2 Controls 30 0 1709039.536815
Input SUBJECT3 Controls 29 0 1423097.816203
Input SUBJECT4 Controls 31 1 1524690.026713
...

When I try to run mri_glmfit I get the following error even though I specify DOSS:

$ mri_glmfit --fsgd SUBJECT1_vs_allControls.fsgd doss [...]

gdfRead(): reading SUBJECT1_vs_allControls.fsgd
WARNING: variable 1 is "Gender" which is often a discrete factor
The proper way to handle discrete factors is to create classes.
See https://surfer.nmr.mgh.harvard.edu/fswiki/FsgdExamples
INFO: DeMeanFlag keyword not found, DeMeaning will NOT be done.
Continuous Variable Means (all subjects)
0 Age 28.6875 6.36611
1 Gender 0.46875 0.499022
2 eTIV 1.51444e+06 125811
Class Size and Means of each Continuous Variable
1 Test 1 50.0000 1.0000 1497422.2500
2 Controls 31 28.0000 0.4516 1514993.8589
ERROR: Class Test has 1 members. With 3 variables and using DODS, you need at least 4 members

How do I get mri_glmfit to use DOSS, or do I have to specify the design matrix by hand in this case?

Thank you!

Best wishes
Cornelius