Hello, I have some questions on doing group comparisons with thickness, area and volume. Many thanks in advance for any help!
1) For a DOSS design with group and gender as categorical factors, I see that an interaction contrast ("Is there a group-gender interaction in the mean thickness?") still exists - but what does this contrast mean, given that DOSS by definition doesn't allow for interactions?
2) it makes sense that measures such as thickness are analysed vertex-wise in QDEC, however what does it mean when the dependent variable is area or volume - measures that do not make physical sense for a single vertex but only at the level of a region consisting of *several* vertices?
3) For values extracted from atlas regions with aparcstats2table, it seems that the product of the extracted CT and area is in the same order of magnitude as the extracted volume, but never really the same or even close - why, when the volume of a region should theoretically be the product of its surface area by its thickness?
Tudor