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