FreeSurfers,
I have been analyzing my qdec data in version 5.0 and have some interesting although somewhat confusing results. Basically I have run a very simple analysis with DODS and DOSS. My discrete factor is group and my covariate is age, about as simple as can be.
When I look at the results for DODS I get:
thickness-age correlation (accounting for group)---result: much of brain significant group difference (I assume controlling for age, but it doesn't say explicitly)--result: one small roi significant thickness-age correlation group difference--result: one small roi spatially adjacent to group difference roi
When I run DOSS I get:
thickness-age correlation (accounting for group)---result: much of brain significant group difference (I assume controlling for age, but it doesn't say explicitly)--result: much of brain significant thickness-age correlation group difference--result: much of brain significant
I am mostly surprised by how much larger the (group difference), and the (thickness-age correlation group difference) increase with the DOSS method. I am also not quite how to interpret the thickness-age correlation group difference in DOSS. I was thinking the DOSS method constrained both groups to have the "same slope" and so I was expecting to get nothing for difference in thickness-age correlation difference by group; isn't this suggesting my two groups have significantly different ageXthickness slopes even though they are constrained to have the same slope by the DOSS method? It would almost make more sense to me if the results were reversed between DOSS and DODS. If I had a large thicknessXage correlation group difference using the DODS method which allows for different slopes. Thanks for any enlightenment.
Chris Bell University of Minnesota