Dear all,

I have calculated the correlation between 2 measurements/variables. The result of this correlation is a voxel-wise dataset that shows the correlation for each voxel in the brain. Furthermore, I use different ROIs in the brain.

What I would like to do now is to statistically compare if various correlations between different ROIs significantly differ. This means that I would like to compare different correlations. Let me provide you with an example:
- Does the (previously calculated) correlation of the 2 variables in ROIs 1 vs. 2 significantly differ vs. the correlation of both variables in ROI 3 vs. 4?

Consequently, three steps are required:
1. Calculate the correlation between ROI 1 and ROI 2.
2. Calculate the correlation between ROI 3 and ROI 4.
3. Now test if the two correlation results of both ROI comparisons differ significantly.

What would be the best AFNI program to perform these steps? I used 3dtcorrelate and 3dttest++, but it seems that something is wrong. I am breaking my head over this for hours now. For example, the correlation of ROI 1 and ROI 2 does not really overlap with the other correlation of ROI 3 and ROI 4. In this case, does it even make sense to compare the correlation in step 3 between the two correlations that I calculated in step 1 and 2? Is it logically reasonable? And is 3dttest++ the correct AFNI program to perform step 3?

-------------------------------------------------------------------------------------------------------------------------------------

I would like to specify my question, or ask a bit of a different question. I think that would make things easier. The setup is as follows:
- The correlation between 2 variables was calculated. For each subject, I would have a file in AFNI format (BRIK and HEAD) that shows me the correlation for each voxel.
- This correlation between 2 variables was calculated via 3dTcorrelate for two different ROIs.

Would 3dttest++ be the appropriate tool to now calculate if there is a significant difference between both correlations, i.e., between correlation from ROI 1 and correlation from ROI 2? I wonder if my question is already ill-posed, especially when both ROIs show no real overlap in the brain.



Edited 2 time(s). Last edit at 11/17/2021 02:34AM by Philipp.