Hi, Katie-

taking a step back:
We often recommend showing beta weights (coefficient values) and using the statistics as a threshold, when appropriate; for example, if you have a t-stat volume, you should have a Coef volume in your statistical output, so you can do this (but the F-stat doesn't have an accompanying Coef volume for this). Other practices in the field are to show the statistic AND use it to threshold. We feel this misses out important modeling information---details are here:
[pubmed.ncbi.nlm.nih.gov]
... and ways to do this in the AFNI GUI are described in this AFNI Academy/Bootcamp video:
[www.youtube.com]

That is why 3dClusterize has both a "-ithr .." and and "-idat .." option: you can input *both* a data (=Coef) volume, and a stat volume. The stat will be used for thresholding, and you can output a map of the data volume with "-pref_dat ..". The "-pref_map .." volume is a map of the ROIs that survive your thresolding. If you want to see the statistics in each of these locations, you can use the PREF_MAP dset (yours is called "ETAC.clust.order.Nwarp_FINAL.nii.gz") and the DSET_STAT (yours would be "TTnew.etac3.ETACmaskALL.global.2sid.5perc_Nwarp.nii[1]", with quotes used in the command here):

3dcalc -a PREF_MAP -b DSET_STAT -expr 'step(a)*b' -prefix DSET_STAT_IN_ROIS

or, in your case here:

3dcalc  \
   -a  ETAC.clust.order.Nwarp_FINAL.nii.gz \
   -b "TTnew.etac3.ETACmaskALL.global.2sid.5perc_Nwarp.nii[1]"  \
    -expr 'step(a)*b'  \
    -prefix SOMETHING.nii

You can take an ROI map and a separate dset and find the mean/stdev/etc. values of that other dset, per ROI, using 3dROIstats. For example,

3dROIstats -mask PREF_MAP DSET_STAT

.... would calculate the average value within DSET_STAT for each ROI in PREF_MAP, and report it on the command line. Rr, for your data:

3dROIstats \
    -mask ETAC.clust.order.Nwarp_FINAL.nii.gz \
   "TTnew.etac3.ETACmaskALL.global.2sid.5perc_Nwarp.nii[1]"

(you might want to try adding "-quiet", too, to remove non-numerical text output.)

Lots of things can be calculated; here are a few from the program help:

-nzmean       Compute the mean using only non_zero voxels.  Implies
                 the opposite for the normal mean computed
  -nzsum        Compute the sum using only non_zero voxels.  
  -nzvoxels     Compute the number of non_zero voxels
  -nzvolume     Compute the volume of non-zero voxels
  -minmax       Compute the min/max of all voxels
  -nzminmax     Compute the min/max of non_zero voxels
  -sigma        Compute the standard deviation of all voxels
  -nzsigma      Compute the standard deviation of all non_zero voxels
  -median       Compute the median of all voxels.
  -nzmedian     Compute the median of non_zero voxels.

Another AFNI Academy video that discusses this (among other ROI tools) is:
[www.youtube.com]

--pt