Hi Afni experts,
I ran a paired ttest (subjects in same order for group A and B) and used -BminusA such that group B is subtracted from group A. From this, the negative blue clusters suggest GroupA > GroupB, and positive red clusters are GroupA < GroupB. I then created a cluster mask of the significant voxels, and then extracted nonzero mean values. When looking at the raw nonzero mean values (3dROIstats with cluster as mask), the raw GroupB mean values were larger than raw GroupA mean values, suggesting that GroupA < GroupB, even though the cluster tstat suggests Group B > Group A. Is there a reason why the ttest directionality and raw values do not match? Does a paired ttest default to only AminusB even if -BminusA is specified?

Command:
3dttest++ -prefix ./3dttest/PostvsPre -BminusA -setA Pre Sub1 'Pre/Sub1.nii[0]' Sub2 'Pre/Sub2.nii[0]' Sub3 'Pre/Sub3.nii[0]' -setB Post Sub1_2 'Post/Sub1_2.nii[0]' Sub2_2 'Post/Sub2_2.nii[0]' Sub3_2 'Post/Sub3_2.nii[0]' -mask ~/Documents/ROI_1mm/mask.nii -paired -center SAME


Thanks,
Ajay



Edited 3 time(s). Last edit at 10/13/2016 02:16AM by AjaySK.