afni.nimh.nih.gov

Hello,

I'm a new user to AFNI, so please forgive me if there's an obvious error on my part. I am trying to do a 2-sample t-test with 3dttest++ and want to use ETAC for cluster correction. I have two groups: depressed (MDD) and control (HC) subjects, so this group analysis compares the mean difference MDD - HC.

When I look at the 3dttest++ output file, specifically the BRIK that displays the mean difference between groups -- (MDD - HC) -- there are both positive and negative differences across the brain. See image below (apologies for its large size):



Specifically, in the voxel selected, the difference is positive between MDD - HC. However, this same voxel is included as a significant voxel in the 1-sided t-test 1neg mask that ETAC gave:



and there are no voxels that are significant for the 1-sided positive 1pos t-test mask that ETAC creates:



I checked the 3dttest++ outputs from the smoothed data to see if this is an artifact of smoothing, but this particular voxel seems to have positive differences at the smoothing levels I gave to ETAC (0, 4, 6, 8).

This is the command I used to run the code:

---

command = ("3dttest++ -setA {0} ".format(MDD_subj_str) +
"-setB {0} ".format(HC_subj_str) +
"-prefix {0}/ses-03_minus_ses-01/ses-03_minus_ses-01_stats_{1}_ACC_dlPFC_mask.ttest.nii.gz ".format(second_level,BRIK_KEY[BRIK]) +
"-AminusB "
"-mask {0} ".format(dlPFC_mask) +
"-covariates {0} ".format(covar_file) +
"-prefix_clustsim ses-03_minus_ses-01_stats_{0}_ACC_dlPFC_mask ".format(BRIK_KEY[BRIK]) +
"-ETAC -ETAC_blur 0 4 6 8 " +
"-ETAC_opt NN=2:sid=1:hpow=0:name=test1:pthr=0.01/0.001/10:fpr=5"
)

---

Is there something I'm missing here?

Thanks so much!