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 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?
- how are the volume measurements provided in aseg.volume different from
the ones done obtained with a VBM analysis?
- 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?
- 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
- 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?
- 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?
Many thanks in advance!!
Tudor