Hi Rick,

Thank you for your response. I redacted the actual subject names to avoid putting confidential info on the internet. So 1NNN may be 1234, or 1432, and none of them are identical. However, just in case it was a formatting issue with how the subject was called, I also tried the following (subject names have now been changed to sequential numbers, to avoid confusion), and it also did not work. All files, including the COVAR_FILE are in the same directory, and values in the same row are separated by tabs.

ttest script:


3dttest++ -prefix groupOutput -covariates COVAR_FILE -cmeth MEAN \
-setA
1 1_fcmp_poscing-z-mni-rv.nii \
2 2_fcmp_poscing-z-mni-rv.nii \
3 3_fcmp_poscing-z-mni-rv.nii \
4 4_fcmp_poscing-z-mni-rv.nii \
5 5_fcmp_poscing-z-mni-rv.nii \
6 6_fcmp_poscing-z-mni-rv.nii \
7 7_fcmp_poscing-z-mni-rv.nii \
8 8_fcmp_poscing-z-mni-rv.nii \
9 9_fcmp_poscing-z-mni-rv.nii \
10 10_fcmp_poscing-z-mni-rv.nii \
11 11_fcmp_poscing-z-mni-rv.nii \
12 12_fcmp_poscing-z-mni-rv.nii \
13 13_fcmp_poscing-z-mni-rv.nii \
14 14_fcmp_poscing-z-mni-rv.nii \
15 15_fcmp_poscing-z-mni-rv.nii \
16 16_fcmp_poscing-z-mni-rv.nii \
17 17_fcmp_poscing-z-mni-rv.nii \
18 18_fcmp_poscing-z-mni-rv.nii \
19 19_fcmp_poscing-z-mni-rv.nii \
20 20_fcmp_poscing-z-mni-rv.nii



Covariate Text File:

subject AgeFirst

1 15
2 20
3 17
4 18
5 17
6 25
7 17
8 20
9 17
10 20
11 18
12 21
13 17
14 14
15 19
16 20
17 16
18 18
19 15
20 16


Thanks again for your help, and I appreciate any further insight you may have to offer.