ETAC in 3dttest++ with covariates

Can the ETAC option in 3dttest++ be used with covariates? I am interested in looking at the correlation between a symptom measure and BOLD signal in a task and have been using Clustsim, but would like to supplement the analyses with the new ETAC method.

Thank you!

Hi AFNI staff.

This might’ve gotten lost in the shuffle around Thanksgiving. Any advice on using ETAC with covariate measures would be much appreciated.


Yes, it can. I do not believe it cares about such things, and simply runs the permutation tests from the residuals of the regression/ttest.

  • rick

I’m actually trying to runs something similar. However the two etac masks did not change if I run the t-test with or without covariates. Does this mean that covariates did not affect the t-test? However, what I expected is a mask for the covariates bricks which I did not have.

I wanted to follow up on this thread. I ran a 3dttest++ with ETAC and the ETAC masks reflect the activity in the subbrick corresponding to the t-statistic map for the mean effect, not the t-statistic map for the covariate. I want to apply ETAC to the map that shows me the voxels where there is a relationship between task activity and a clinical correlate (i.e., voxels where there is a relationship between alcohol cue reactivity and subjects' AUDIT scores). Can someone please tell us how to get ETAC to apply to the covariate map?

This is a good question, and I am not even sure it is possible.

From what I know, ETAC generates random clusters from tests on permuted volumes from the residuals of a given test. Importantly, that would suggest there is only a single ETAC result for the test that includes both the main effect and the covariates. ETAC would apply to both at once, effectively, where the resulting mask might be a little different than one generated from the same test without any covariates.

If this is the case, I do not see how it would be possible to have a separate ETAC result to apply to just covariates. Though perhaps there is an aspect that I am missing...

  • rick