On 04/28/2012 09:45 PM, Mahinda Yogarajah wrote:
Dear Experts,
I had 2 questions with regard to vertex wise analysis using qdec.
- How should one interpret the dependent variables area/pial area and
volume when comparing 2 groups with qdec and a vertex wise (as opposed to ROI based) analysis - or are they uninterpretable in this context ? I read briefly about areal as an alternative measure - could someone explain the difference, and how thickness, volume and area related to one another ?
volume = area * thickness. The "area" of a vertex is the average of the triangles that surround it. For a group analysis, you can think of it as drawing a small circle around a vertex in fsaverage space and asking how big that circle is in each individual subject.
- When running monte-carlo cluster wise multiple correction in qdec -
if one finds a significant cluster is it ok to view them within qdec by highlighting the "mc-z ... " file in the analysis result box, and then changing the minimum threshold to whatever value one selected for the monte carlo simulation ?
No, the mc-z output has values equal to the cluster-wise p-value, so it is not appropriate to apply the vertex-wise threshold.
The reason I ask is that the text ouput given by the monte carlo cluster analysis gives different coorinates in the cluster table to that output given when one clicks on the "find clusters and go to max" button ...
Are you using the "abs" when you do the clustering? Is is possible that it found a negative peak in the table but qdec goes to the positive peak?
Thanks.
Mahinda
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