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I have a question regarding how to graph results that came from a vertex
wise analysis using the command mri_glmfit and mri_glmfit-sim.

I was interested in investigating an interaction effect between groups and
my variable of interest (continuous) while co-varying for three nuisance
variables. After running mri_glmfit and mri_glmfit-sim to correct for
multiple comparisons. I visualized the results and found significant

I'm interested in graphing these results. Based on archived questions to
this mailing list the individual values for each cluster can be found
within the ocn.dat file and the cluster information can be found in the
summary file. My analysis looked at volume, thickness and surface area.
Since mean volume and area is difficult to interpret I want to convert the
values to a total measure. It has been suggested in the past this can be
done by multiplying each individuals values within the ocn.dat file by the
number of vertices the cluster has. However, from my understanding this
could be done by altering the mri_segstats command (that mri_glmfit-sim
automatically runs) to include the --accumulate option.

When I do these methods to convert mean area and volume to total area and
volume the results are different.

My first question is 1) Shouldn't these values be identical? The values
from multiplying mean volume by number of vertices are roughly around 3500.
Whereas using the --accumulate in mri_segstats are around 2500. What could
be causing this discrepancy?

2) If my cluster has a size of 1500 mm^2 (in a model for area) does it make
sense that every individual's values after extraction and conversion to
total area are larger than the cluster size?

3) ocn.dat files are the input values meaning they're raw and would need to
be corrected in a statistically (in a similar way that I modeled it in
freesurfer) before graphing right?
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