Hi Tudor,

if you are trying to just construct a mean thickness map on a subset of your data (e.g. group 1, tp 1) then you could map and smooth the data using
mris_preproc
The easiest way to pass the subjects is to manually split your longitudinal qdec file into smaller ones to contain only the entries of group1 and tp1 etc and then pass this via the --qdec-long flag.
Once the data is smoothed and mapped to fsaverage, you can use
mri_concat
to compute the mean of the stack (flag --mean). You can visualize it in tksurfer or freeview.

Best, Martin

On 10/02/2014 10:29 AM, Tudor Popescu wrote:
Dear FS list (dear Martin),

I have a 3 groups x 2 timepoints data set, and I did analyses in QDEC comparing my groups pairwise (2 at a time) in terms of the pre-to-post percentage change (pc1) in various surface-based metrics like thickness and area.

Since a group contrast is a bit difficult for readers to interpret (it would read "where is the percentage change from pre to post greater for group 1 than for group 2?"), I am wondering what is, in fact, best to report, aside from showing images of the significant clusters. What commands would I have to use, exactly, to for instnace, compute the group means for pre and for post values for e.g. thickness, i.e. absolute values rather than differences? I think I only have the pc1's calculated, since if I select thickness (rather than thickness-pc1) in QDEC, it tells me it cannot find the smoothed files.

Thanks!


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-- 
Dr. Martin Reuter

Instructor in Neurology
  Harvard Medical School
Assistant in Neuroscience
  Dept. of Radiology, Massachusetts General Hospital
  Dept. of Neurology, Massachusetts General Hospital
Research Affiliate
  Computer Science and Artificial Intelligence Lab,
  Dept. of Electrical Engineering and Computer Science,
  Massachusetts Institute of Technology

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