On 03/28/2013 03:53 PM, Tudor Popescu wrote:
I was wondering if anybody is able to help with (any one of) these questions? That would be really helpful, as I could not find an answer on the wiki.
Many thanks in advance!
On 26 March 2013 20:44, Tudor Popescu <tudor3@gmail.com mailto:tudor3@gmail.com> wrote:
Hi everyone, My QDEC analysis ran into an error message that seems to be a "classic" (and, so far, it seems unsolved), from mri_concat, which I've described in a separate message, just sent. I have, however, more theoretical questions about QDEC, which I hope some kind soul will help me with: - why does QDEC only provide the volume of /subcortical/ structures under StatsDataImport/aseg.volume, when the automatic GM/WM segmentation is done for the entire brain, not just for subcortical regions?
No reason in particular. You can add them into the qdec table.
- how are the volume measurements provided in aseg.volume different from the ones done obtained with a VBM analysis?
Does VBM give segmentation volumes? I thought it was voxel-wise exploratory.
- why is /volume /the result of /segmentation /(aseg.volume) whereas /thickness /derives from /parcelation /(rh.aparc.thickness)? Is it not the case that both operations (segmentation+parcellation) are necessary to calculate volume as well as thickness?
You can get volume from parcellations too (this is supplied in the ?h.apac.stats file). You can't get thickness from non-surface structures like amygdala.
- how is a QDEC thickness analysis different from a regular AN(C)OVA in which you are interested in main and interaction effects of the IVs on the DV? I ask this because some of the questions that appear in QDEC's Analysis Results tab – e.g. "is the correlation between (DV) and (IV) different from zero?" – would not (I think) be directly answerable by an ANOVA
Often times they are the same, depends on the contrast. I don't know what IV and DV are so I can't answer your specific question.
- would the same type of ANOVA done by QDEC be doable by extracting the values of the DV for each subject (using e.g. /aseg.volume/) and then doing the ANOVA in e.g. SPSS? If so, when would you do one versus the other?
Yes. QDEC is an exploratory voxel-based method so effects don't have to lie cleanly within an ROI boundary.
- why is it that only continuous factors (e.g. age) can be taken in the analysis as nuisance factors, when discrete variables (e.g. gender) might also be irrelevant for a particular analysis and thus belong to the Nuisance Factor list?
It is just a matter of convenience in making the contrasts. ie, it is easy to extend our contrast making code to add nuisance continuous variables doug
Many thanks in advance!! Tudor
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